Encoding method, decoding method, and processing method

ABSTRACT

An encoding method includes: determining a merge mode to be applied to a current block, the merge mode including a sub-block merge mode and a first merge mode, wherein in the merge mode, inter-prediction parameters are inferred from a neighboring block neighboring the current block, and wherein in the sub-block merge mode, the current block includes a plurality of sub-blocks, and inter-prediction parameters are provided for each of the plurality of sub-blocks; in response to the merge mode being determined to be the first merge mode, generating a prediction image for the current block by performing a bi-directional optical flow prediction process, wherein the bi-directional optical flow prediction process uses a spatial gradient for the current block; and in response to the merge mode being determined to be the sub-block merge mode, generating a prediction image for the current block by not performing the bi-directional optical flow prediction process.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. continuation application of U.S. patentapplication Ser. No. 17/389,010, filed on Jul. 29, 2021, which is a U.S.continuation application of U.S. patent application Ser. No. 16/799,315,filed on Feb. 24, 2020, which is a U.S. continuation application of PCTInternational Patent Application Number PCT/JP2019/003265 filed on Jan.30, 2019, claiming the benefit of priority of U.S. Provisional PatentApplication No. 62/626,974 filed on Feb. 6, 2018, the entire contents ofwhich are hereby incorporated by reference.

BACKGROUND 1. Technical Field

The present disclosure relates to an encoder and so on that encodesvideo.

2. Description of the Related Art

As a video coding standard, there has been H.265 which is also referredto as High-Efficiency Video Coding (HEVC) (NPL1: H.265(ISO/IEC 23008-2HEVC)/HEVC(High Efficiency Video Coding)).

SUMMARY

An encoding method according to an aspect of the present disclosureincludes determining a merge mode to be applied to a current block, themerge mode including a sub-block merge mode and a first merge modedifferent from the sub-block merge mode, wherein in the merge mode,inter-prediction parameters are inferred from a neighboring blockneighboring the current block, and wherein in the sub-block merge mode,the current block includes a plurality of sub-blocks, andinter-prediction parameters are provided for each of the plurality ofsub-blocks; in response to the merge mode being determined to be thefirst merge mode, generating a prediction image for the current block byperforming a bi-directional optical flow prediction process, wherein thebi-directional optical flow prediction process uses a spatial gradientfor the current block; and in response to the merge mode beingdetermined to be the sub-block merge mode, generating a prediction imagefor the current block by not performing the bi-directional optical flowprediction process.

Note that these general and specific aspects may be implemented using asystem, a device, a method, an integrated circuit, a computer program, anon-transitory computer-readable recording medium such as a CD-ROM, orany combination of systems, devices, methods, integrated circuits,computer programs or recording media.

BRIEF DESCRIPTION OF DRAWINGS

These and other objects, advantages and features of the disclosure willbecome apparent from the following description thereof taken inconjunction with the accompanying drawings that illustrate a specificembodiment of the present disclosure.

FIG. 1 is a block diagram illustrating a functional configuration of anencoder according to Embodiment 1;

FIG. 2 illustrates one example of block splitting according toEmbodiment 1;

FIG. 3 is a chart indicating transform basis functions for eachtransform type;

FIG. 4A illustrates one example of a filter shape used in ALF;

FIG. 4B illustrates another example of a filter shape used in ALF;

FIG. 4C illustrates another example of a filter shape used in ALF;

FIG. 5A illustrates 67 intra prediction modes used in intra prediction;

FIG. 5B is a flow chart for illustrating an outline of a predictionimage correction process performed via OBMC processing;

FIG. 5C is a conceptual diagram for illustrating an outline of aprediction image correction process performed via OBMC processing;

FIG. 5D illustrates one example of FRUC;

FIG. 6 is for illustrating pattern matching (bilateral matching) betweentwo blocks along a motion trajectory;

FIG. 7 is for illustrating pattern matching (template matching) betweena template in the current picture and a block in a reference picture;

FIG. 8 is for illustrating a model assuming uniform linear motion;

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks;

FIG. 9B is for illustrating an outline of a process for deriving amotion vector via merge mode;

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing;

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing;

FIG. 10 is a block diagram illustrating a functional configuration of adecoder according to Embodiment 1;

FIG. 11 is a flow chart for illustrating one example of the operationperformed by the encoder and the decoder according to the primaryaspect;

FIG. 12 is a flow chart for illustrating another example of theoperation performed by the encoder and the decoder according to theprimary aspect;

FIG. 13 is a diagram illustrating one example of a method fordetermining a motion vector of each sub-block in ATMVP mode;

FIG. 14 is a diagram illustrating one example of a method fordetermining a motion vector of each sub-block in STMVP mode;

FIG. 15 is a block diagram illustrating an implementation example of theencoder according to Embodiment 1;

FIG. 16 is a flow chart for illustrating an operation example of theencoder according to Embodiment 1;

FIG. 17 is a block diagram illustrating an implementation example of thedecoder according to Embodiment 1;

FIG. 18 is a flow chart for illustrating an operation example of thedecoder according to Embodiment 1;

FIG. 19 illustrates an overall configuration of a content providingsystem for implementing a content distribution service;

FIG. 20 illustrates one example of an encoding structure in scalableencoding;

FIG. 21 illustrates one example of an encoding structure in scalableencoding;

FIG. 22 illustrates an example of a display screen of a web page;

FIG. 23 illustrates an example of a display screen of a web page;

FIG. 24 illustrates one example of a smartphone; and

FIG. 25 is a block diagram illustrating a configuration example of asmartphone.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(Underlying Knowledge Forming Basis of the Present Disclosure)

For example, in the video coding, etc., when encoding a video on which afurther subdivided prediction process is performed while preventing anincrease in the amount of processing, an encoder that encodes a videoderives a prediction error by subtracting a prediction image from animage included in the video. Subsequently, the encoder frequency-conversand quantizes the prediction error, and encodes the resultant as imagedata. In doing so, with respect to a motion in a current unit to beencoded such as a block included in a video, when (i) motion predictionis performed for each block or each sub-block included in the each blockand (ii) motion correction is performed in a further subdivided unit,the accuracy of coding is improved.

However, when a properly-subdivided prediction process is not performedin coding the block included in the video, etc., an increase in theamount of processing occurs, thereby reducing the coding efficiency.

In view of this, an encoder according to an aspect of the presentdisclosure may be an encoder that encodes a video by performing aprediction process. The encoder may include: circuitry; and memory, inwhich using the memory, the circuitry: determines which mode is used toperform the prediction process, among a plurality of modes including afirst mode in which the prediction process is performed based on amotion vector of each block in the video and a second mode in which theprediction process is performed based on a motion vector of eachsub-block obtained by splitting the block; when the prediction processis performed in the first mode, determines whether to perform acorrection process on a prediction image using a spatial gradient ofpixel values in the prediction image obtained by performing theprediction process, and performs the correction process when it isdetermined to perform the correction process; and when the predictionprocess is performed in the second mode, does not perform the correctionprocess.

With this, the encoder uses a per-subdivided-unit motion correction incombination with the motion prediction for each block, and thus thecoding efficiency is improved. Furthermore, the motion prediction foreach sub-block has a greater amount of processing than the motionprediction for each block, and thus when the motion prediction isperformed for each sub-block, the encoder does not perform theper-subdivided-unit motion correction. Thus, the encoder performs theper-subdivided-unit motion prediction only for the motion prediction foreach block, and thereby it is possible to reduce the amount ofprocessing while maintaining the coding efficiency. Accordingly, theencoder can perform a further subdivided prediction process whilepreventing an increase in the amount of processing.

For example, the first mode and the second mode may be included in amerge mode in which a motion vector predictor is used as a motionvector.

With this, the encoder can speed up a process for deriving a predictionsample set in the merge mode.

Furthermore, for example, the circuitry: when the prediction process isperformed in the first mode, may encode determination result informationindicating a result of the determining whether to perform the correctionprocess; and when the prediction process is performed in the secondmode, need not encode the determination result information.

With this, the encoder can reduce the encoded amount.

Furthermore, for example, the correction process may be a bi-directionaloptical flow (BIO) process.

With this, the encoder can correct the prediction image using aper-subdivided-unit correction value in the prediction image generatedby deriving the motion vector for each block.

Furthermore, for example, the second mode may be an advanced temporalmotion vector prediction (ATMVP) mode.

With this, the encoder need not perform the per-subdivided-unit motioncorrection in ATMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be a spatial-temporalmotion vector prediction (STMVP) mode.

With this, the encoder need not perform the per-subdivided-unit motioncorrection in STMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be an affine motioncompensation prediction mode.

With this, the encoder need not perform the per-subdivided-unit motioncorrection in affine mode, and thus the amount of processing is reduced.

Furthermore, a decoder according to an aspect of the present disclosuremay be a decoder that decodes a video by performing a predictionprocess. The decoder may include: circuitry; and memory, in which usingthe memory, the circuitry: determines which mode is used to perform theprediction process, among a plurality of modes including a first mode inwhich the prediction process is performed based on a motion vector ofeach block in the video and a second mode in which the predictionprocess is performed based on a motion vector of each sub-block obtainedby splitting the block; when the prediction process is performed in thefirst mode, determines whether to perform a correction process on aprediction image using a spatial gradient of pixel values in theprediction image obtained by performing the prediction process, andperforms the correction process when it is determined to perform thecorrection process; and when the prediction process is performed in thesecond mode, does not perform the correction process.

With this, the decoder uses a per-subdivided-unit motion correction incombination with the motion prediction for each block, and thus thecoding efficiency is improved. Furthermore, the motion prediction foreach sub-block has a greater amount of processing than the motionprediction for each block, and thus when the motion prediction isperformed for each sub-block, the decoder does not perform theper-subdivided-unit motion correction. Thus, the decoder performs theper-subdivided-unit motion prediction only for the motion prediction foreach block, and thereby it is possible to reduce the amount ofprocessing while maintaining the coding efficiency. Accordingly, thedecoder can perform a further subdivided prediction process whilepreventing an increase in the amount of processing.

For example, the first mode and the second mode may be included in amerge mode in which a motion vector predictor is used as a motionvector.

With this, the decoder can speed up a process for deriving theprediction sample set in the merge mode.

Furthermore, for example, the circuitry: when the prediction process isperformed in the first mode, may decode determination result informationindicating a result of the determining whether to perform the correctionprocess; and when the prediction process is performed in the secondmode, need not decode the determination result information.

With this, the decoder can improve the processing efficiency.

Furthermore, for example, the correction process may be a BIO process.

With this, the decoder can correct the prediction image using aper-subdivided-unit correction value in the prediction image generatedby deriving the motion vector for each block.

Furthermore, for example, the second mode may be an ATMVP mode.

With this, the decoder need not perform the per-subdivided-unit motioncorrection in ATMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be a STMVP mode.

With this, the decoder need not perform the per-subdivided-unit motioncorrection in STMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be an affine motioncompensation prediction mode.

With this, the decoder need not perform the per-subdivided-unit motioncorrection in affine mode, and thus the amount of processing is reduced.

Furthermore, an encoding method according to an aspect of the presentdisclosure may be an encoding method for encoding a video by performinga prediction process. The encoding method may include: determining whichmode is used to perform the prediction process, among a plurality ofmodes including a first mode in which the prediction process isperformed based on a motion vector of each block in the video and asecond mode in which the prediction process is performed based on amotion vector of each sub-block obtained by splitting the block; whenthe prediction process is performed in the first mode, determiningwhether to perform a correction process on a prediction image using aspatial gradient of pixel values in the prediction image obtained byperforming the prediction process, and performing the correction processwhen it is determined to perform the correction process; and when theprediction process is performed in the second mode, not performing thecorrection process.

With this, the per-subdivided-unit motion correction is used incombination with the motion prediction for each block, and thus thecoding efficiency is improved. Furthermore, the motion prediction foreach sub-block has a greater amount of processing than the motionprediction for each block, and thus in the encoding method, when themotion prediction is performed for each sub-block, theper-subdivided-unit motion correction is not performed. Thus, accordingto the encoding method, the per-subdivided-unit motion prediction isperformed only for the motion prediction for each block, and thereby itis possible to reduce the amount of processing while maintaining thecoding efficiency. Accordingly, according to the encoding method, afurther subdivided prediction process can be performed while preventingan increase in the amount of processing.

Alternatively, a decoding method according to an aspect of the presentdisclosure may be a decoding method for decoding a video by performing aprediction process. The decoding method may include: determining whichmode is used to perform the prediction process, among a plurality ofmodes including a first mode in which the prediction process isperformed based on a motion vector of each block in the video and asecond mode in which the prediction process is performed based on amotion vector of each sub-block obtained by splitting the block; whenthe prediction process is performed in the first mode, determiningwhether to perform a correction process on a prediction image using aspatial gradient of pixel values in the prediction image obtained byperforming the prediction process, and performing the correction processwhen it is determined to perform the correction process; and when theprediction process is performed in the second mode, not performing thecorrection process.

With this, the per-subdivided-unit motion correction is used incombination with the motion prediction for each block, and thus thecoding efficiency is improved. Furthermore, the motion prediction foreach sub-block has a greater amount of processing than the motionprediction for each block, and thus in the decoding method, when themotion prediction is performed for each sub-block, theper-subdivided-unit motion correction is not performed. Thus, accordingto the decoding method, the per-subdivided-unit motion prediction isperformed only for the motion prediction for each block, and thereby itis possible to reduce the amount of processing while maintaining thecoding efficiency. Accordingly, according to the decoding method, afurther subdivided prediction process can be performed while preventingan increase in the amount of processing.

Furthermore, for example, the encoder according to an aspect of thepresent disclosure is an encoder that encodes a video, and may include asplitter, an intra predictor, an inter predictor, a transformer, aquantizer, an entropy encoder, and a loop filter.

The splitter may split a picture included in the video into multipleblocks. The intra predictor may perform intra prediction on a blockincluded in the blocks. The inter predictor may perform inter predictionon the block. The transformer may transform a prediction error betweenan original image and a prediction image obtained through the intraprediction or the inter prediction to generate a transform coefficient.The quantizer may quantize the transform coefficient to generate aquantization coefficient. The entropy encoder may encode thequantization coefficient to generate an encoded bitstream. The loopfilter may apply a filter to a reconstructed image generated using theprediction image.

For example, the inter predictor: determines which mode is used toperform the prediction process, among a plurality of modes including afirst mode in which the prediction process is performed based on amotion vector of each block in the video and a second mode in which theprediction process is performed based on a motion vector of eachsub-block obtained by splitting the block; when the prediction processis performed in the first mode, determines whether to perform acorrection process on a prediction image using a spatial gradient ofpixel values in the prediction image obtained by performing theprediction process, and performs the correction process when it isdetermined to perform the correction process; and when the predictionprocess is performed in the second mode, does not perform the correctionprocess.

Furthermore, for example, the decoder according to an aspect of thepresent disclosure is a decoder that decodes a video, and may include anentropy decoder, an inverse quantizer, an inverse transformer, an intrapredictor, an inter predictor, and a loop filter.

The entropy decoder may decode the quantization coefficient of a blockin a picture from the encoded bitstream. The inverse quantizer mayinverse quantize the quantization coefficient to obtain a transformcoefficient. The inverse transformer may inverse transform the transformcoefficient to obtain a prediction error. The intra predictor mayperform intra prediction on the block. The inter predictor may performinter prediction on the block. The loop filter may apply a filter to areconstructed image generated using the prediction error and theprediction image obtained through the intra prediction or the interprediction.

For example, the inter predictor: determines which mode is used toperform the prediction process, among a plurality of modes including afirst mode in which the prediction process is performed based on amotion vector of each block in the video and a second mode in which theprediction process is performed based on a motion vector of eachsub-block obtained by splitting the block; when the prediction processis performed in the first mode, determines whether to perform acorrection process on a prediction image using a spatial gradient ofpixel values in the prediction image obtained by performing theprediction process, and performs the correction process when it isdetermined to perform the correction process; and when the predictionprocess is performed in the second mode, does not perform the correctionprocess.

Furthermore, these general and specific aspects may be implemented usinga system, a device, a method, an integrated circuit, a computer program,a non-transitory computer-readable recording medium such as a CD-ROM, orany combination of systems, devices, methods, integrated circuits,computer programs or recording media.

Hereinafter, embodiment(s) will be described with reference to thedrawings.

Note that the embodiment(s) described below each show a general orspecific example. The numerical values, shapes, materials, components,the arrangement and connection of the components, steps, order of thesteps, etc., indicated in the following embodiment(s) are mere examples,and therefore are not intended to limit the scope of the claims.Therefore, among the components in the following embodiment(s), thosenot recited in any of the independent claims defining the broadestinventive concepts are described as optional components.

Embodiment 1

First, an outline of Embodiment 1 will be presented. Embodiment 1 is oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in subsequent description of aspects of thepresent disclosure are applicable. Note that Embodiment 1 is merely oneexample of an encoder and a decoder to which the processes and/orconfigurations presented in the description of aspects of the presentdisclosure are applicable. The processes and/or configurations presentedin the description of aspects of the present disclosure can also beimplemented in an encoder and a decoder different from those accordingto Embodiment 1.

When the processes and/or configurations presented in the description ofaspects of the present disclosure are applied to Embodiment 1, forexample, any of the following may be performed.

-   -   (1) regarding the encoder or the decoder according to Embodiment        1, among components included in the encoder or the decoder        according to Embodiment 1, substituting a component        corresponding to a component presented in the description of        aspects of the present disclosure with a component presented in        the description of aspects of the present disclosure;    -   (2) regarding the encoder or the decoder according to Embodiment        1, implementing discretionary changes to functions or        implemented processes performed by one or more components        included in the encoder or the decoder according to Embodiment        1, such as addition, substitution, or removal, etc., of such        functions or implemented processes, then substituting a        component corresponding to a component presented in the        description of aspects of the present disclosure with a        component presented in the description of aspects of the present        disclosure;    -   (3) regarding the method implemented by the encoder or the        decoder according to Embodiment 1, implementing discretionary        changes such as addition of processes and/or substitution,        removal of one or more of the processes included in the method,        and then substituting a processes corresponding to a process        presented in the description of aspects of the present        disclosure with a process presented in the description of        aspects of the present disclosure;    -   (4) combining one or more components included in the encoder or        the decoder according to Embodiment 1 with a component presented        in the description of aspects of the present disclosure, a        component including one or more functions included in a        component presented in the description of aspects of the present        disclosure, or a component that implements one or more processes        implemented by a component presented in the description of        aspects of the present disclosure;    -   (5) combining a component including one or more functions        included in one or more components included in the encoder or        the decoder according to Embodiment 1, or a component that        implements one or more processes implemented by one or more        components included in the encoder or the decoder according to        Embodiment 1 with a component presented in the description of        aspects of the present disclosure, a component including one or        more functions included in a component presented in the        description of aspects of the present disclosure, or a component        that implements one or more processes implemented by a component        presented in the description of aspects of the present        disclosure;    -   (6) regarding the method implemented by the encoder or the        decoder according to Embodiment 1, among processes included in        the method, substituting a process corresponding to a process        presented in the description of aspects of the present        disclosure with a process presented in the description of        aspects of the present disclosure; and    -   (7) combining one or more processes included in the method        implemented by the encoder or the decoder according to        Embodiment 1 with a process presented in the description of        aspects of the present disclosure.

Note that the implementation of the processes and/or configurationspresented in the description of aspects of the present disclosure is notlimited to the above examples. For example, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be implemented in a device used for a purpose differentfrom the moving picture/picture encoder or the moving picture/picturedecoder disclosed in Embodiment 1. Moreover, the processes and/orconfigurations presented in the description of aspects of the presentdisclosure may be independently implemented. Moreover, processes and/orconfigurations described in different aspects may be combined.

[Encoder Outline]

First, the encoder according to Embodiment 1 will be outlined. FIG. 1 isa block diagram illustrating a functional configuration of encoder 100according to Embodiment 1. Encoder 100 is a moving picture/pictureencoder that encodes a moving picture/picture block by block.

As illustrated in FIG. 1 , encoder 100 is a device that encodes apicture block by block, and includes splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, block memory 118, loop filter120, frame memory 122, intra predictor 124, inter predictor 126, andprediction controller 128.

Encoder 100 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as splitter 102, subtractor104, transformer 106, quantizer 108, entropy encoder 110, inversequantizer 112, inverse transformer 114, adder 116, loop filter 120,intra predictor 124, inter predictor 126, and prediction controller 128.Alternatively, encoder 100 may be realized as one or more dedicatedelectronic circuits corresponding to splitter 102, subtractor 104,transformer 106, quantizer 108, entropy encoder 110, inverse quantizer112, inverse transformer 114, adder 116, loop filter 120, intrapredictor 124, inter predictor 126, and prediction controller 128.

Hereinafter, each component included in encoder 100 will be described.

[Splitter]

Splitter 102 splits each picture included in an input moving pictureinto blocks, and outputs each block to subtractor 104. For example,splitter 102 first splits a picture into blocks of a fixed size (forexample, 128×128). The fixed size block is also referred to as codingtree unit (CTU). Splitter 102 then splits each fixed size block intoblocks of variable sizes (for example, 64×64 or smaller), based onrecursive quadtree and/or binary tree block splitting. The variable sizeblock is also referred to as a coding unit (CU), a prediction unit (PU),or a transform unit (TU). Note that in this embodiment, there is no needto differentiate between CU, PU, and TU; all or some of the blocks in apicture may be processed per CU, PU, or TU.

FIG. 2 illustrates one example of block splitting according toEmbodiment 1. In FIG. 2 , the solid lines represent block boundaries ofblocks split by quadtree block splitting, and the dashed lines representblock boundaries of blocks split by binary tree block splitting.

Here, block 10 is a square 128×128 pixel block (128×128 block). This128×128 block 10 is first split into four square 64×64 blocks (quadtreeblock splitting).

The top left 64×64 block is further vertically split into two rectangle32×64 blocks, and the left 32×64 block is further vertically split intotwo rectangle 16×64 blocks (binary tree block splitting). As a result,the top left 64×64 block is split into two 16×64 blocks 11 and 12 andone 32×64 block 13.

The top right 64×64 block is horizontally split into two rectangle 64×32blocks 14 and 15 (binary tree block splitting).

The bottom left 64×64 block is first split into four square 32×32 blocks(quadtree block splitting). The top left block and the bottom rightblock among the four 32×32 blocks are further split. The top left 32×32block is vertically split into two rectangle 16×32 blocks, and the right16×32 block is further horizontally split into two 16×16 blocks (binarytree block splitting). The bottom right 32×32 block is horizontallysplit into two 32×16 blocks (binary tree block splitting). As a result,the bottom left 64×64 block is split into 16×32 block 16, two 16×16blocks 17 and 18, two 32×32 blocks 19 and 20, and two 32×16 blocks 21and 22.

The bottom right 64×64 block 23 is not split.

As described above, in FIG. 2 , block 10 is split into 13 variable sizeblocks 11 through 23 based on recursive quadtree and binary tree blocksplitting. This type of splitting is also referred to as quadtree plusbinary tree (QTBT) splitting.

Note that in FIG. 2 , one block is split into four or two blocks(quadtree or binary tree block splitting), but splitting is not limitedto this example. For example, one block may be split into three blocks(ternary block splitting). Splitting including such ternary blocksplitting is also referred to as multi-type tree (MBT) splitting.

[Subtractor]

Subtractor 104 subtracts a prediction signal (prediction sample) from anoriginal signal (original sample) per block split by splitter 102. Inother words, subtractor 104 calculates prediction errors (also referredto as residuals) of a block to be encoded (hereinafter referred to as acurrent block). Subtractor 104 then outputs the calculated predictionerrors to transformer 106.

The original signal is a signal input into encoder 100, and is a signalrepresenting an image for each picture included in a moving picture (forexample, a luma signal and two chroma signals). Hereinafter, a signalrepresenting an image is also referred to as a sample.

[Transformer]

Transformer 106 transforms spatial domain prediction errors intofrequency domain transform coefficients, and outputs the transformcoefficients to quantizer 108. More specifically, transformer 106applies, for example, a predefined discrete cosine transform (DCT) ordiscrete sine transform (DST) to spatial domain prediction errors.

Note that transformer 106 may adaptively select a transform type fromamong a plurality of transform types, and transform prediction errorsinto transform coefficients by using a transform basis functioncorresponding to the selected transform type. This sort of transform isalso referred to as explicit multiple core transform (EMT) or adaptivemultiple transform (AMT).

The transform types include, for example, DCT-II, DCT-V, DST-I, andDST-VII. FIG. 3 is a chart indicating transform basis functions for eachtransform type. In FIG. 3 , N indicates the number of input pixels. Forexample, selection of a transform type from among the plurality oftransform types may depend on the prediction type (intra prediction andinter prediction), and may depend on intra prediction mode.

Information indicating whether to apply such EMT or AMT (referred to as,for example, an AMT flag) and information indicating the selectedtransform type is signalled at the CU level. Note that the signaling ofsuch information need not be performed at the CU level, and may beperformed at another level (for example, at the sequence level, picturelevel, slice level, tile level, or CTU level).

Moreover, transformer 106 may apply a secondary transform to thetransform coefficients (transform result). Such a secondary transform isalso referred to as adaptive secondary transform (AST) or non-separablesecondary transform (NSST). For example, transformer 106 applies asecondary transform to each sub-block (for example, each 4×4 sub-block)included in the block of the transform coefficients corresponding to theintra prediction errors. Information indicating whether to apply NSSTand information related to the transform matrix used in NSST aresignalled at the CU level. Note that the signaling of such informationneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, or CTU level).

Here, a separable transform is a method in which a transform isperformed a plurality of times by separately performing a transform foreach direction according to the number of dimensions input. Anon-separable transform is a method of performing a collective transformin which two or more dimensions in a multidimensional input arecollectively regarded as a single dimension.

In one example of a non-separable transform, when the input is a 4×4block, the 4×4 block is regarded as a single array including 16components, and the transform applies a 16×16 transform matrix to thearray.

Moreover, similar to above, after an input 4×4 block is regarded as asingle array including 16 components, a transform that performs aplurality of Givens rotations on the array (i.e., a Hypercube-GivensTransform) is also one example of a non-separable transform.

[Quantizer]

Quantizer 108 quantizes the transform coefficients output fromtransformer 106. More specifically, quantizer 108 scans, in apredetermined scanning order, the transform coefficients of the currentblock, and quantizes the scanned transform coefficients based onquantization parameters (QP) corresponding to the transformcoefficients. Quantizer 108 then outputs the quantized transformcoefficients (hereinafter referred to as quantized coefficients) of thecurrent block to entropy encoder 110 and inverse quantizer 112.

A predetermined order is an order for quantizing/inverse quantizingtransform coefficients. For example, a predetermined scanning order isdefined as ascending order of frequency (from low to high frequency) ordescending order of frequency (from high to low frequency).

A quantization parameter is a parameter defining a quantization stepsize (quantization width). For example, if the value of the quantizationparameter increases, the quantization step size also increases. In otherwords, if the value of the quantization parameter increases, thequantization error increases.

[Entropy Encoder]

Entropy encoder 110 generates an encoded signal (encoded bitstream) byvariable length encoding quantized coefficients, which are inputs fromquantizer 108. More specifically, entropy encoder 110, for example,binarizes quantized coefficients and arithmetic encodes the binarysignal.

[Inverse Quantizer]

Inverse quantizer 112 inverse quantizes quantized coefficients, whichare inputs from quantizer 108. More specifically, inverse quantizer 112inverse quantizes, in a predetermined scanning order, quantizedcoefficients of the current block. Inverse quantizer 112 then outputsthe inverse quantized transform coefficients of the current block toinverse transformer 114.

[Inverse Transformer]

Inverse transformer 114 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 112. More specifically, inverse transformer 114 restores theprediction errors of the current block by applying an inverse transformcorresponding to the transform applied by transformer 106 on thetransform coefficients. Inverse transformer 114 then outputs therestored prediction errors to adder 116.

Note that since information is lost in quantization, the restoredprediction errors do not match the prediction errors calculated bysubtractor 104. In other words, the restored prediction errors includequantization errors.

[Adder]

Adder 116 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 114, and prediction samples,which are inputs from prediction controller 128. Adder 116 then outputsthe reconstructed block to block memory 118 and loop filter 120. Areconstructed block is also referred to as a local decoded block.

[Block Memory]

Block memory 118 is storage for storing blocks in a picture to beencoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 118 storesreconstructed blocks output from adder 116.

[Loop Filter]

Loop filter 120 applies a loop filter to blocks reconstructed by adder116, and outputs the filtered reconstructed blocks to frame memory 122.A loop filter is a filter used in an encoding loop (in-loop filter), andincludes, for example, a deblocking filter (DF), a sample adaptiveoffset (SAO), and an adaptive loop filter (ALF).

In ALF, a least square error filter for removing compression artifactsis applied. For example, one filter from among a plurality of filters isselected for each 2×2 sub-block in the current block based on directionand activity of local gradients, and is applied.

More specifically, first, each sub-block (for example, each 2×2sub-block) is categorized into one out of a plurality of classes (forexample, 15 or 25 classes). The classification of the sub-block is basedon gradient directionality and activity. For example, classificationindex C is derived based on gradient directionality D (for example, 0 to2 or 0 to 4) and gradient activity A (for example, 0 to 4) (for example,C=5D+A). Then, based on classification index C, each sub-block iscategorized into one out of a plurality of classes (for example, 15 or25 classes).

For example, gradient directionality D is calculated by comparinggradients of a plurality of directions (for example, the horizontal,vertical, and two diagonal directions). Moreover, for example, gradientactivity A is calculated by summing gradients of a plurality ofdirections and quantizing the sum.

The filter to be used for each sub-block is determined from among theplurality of filters based on the result of such categorization.

The filter shape to be used in ALF is, for example, a circular symmetricfilter shape. FIG. 4A through FIG. 4C illustrate examples of filtershapes used in ALF. FIG. 4A illustrates a 5×5 diamond shape filter, FIG.4B illustrates a 7×7 diamond shape filter, and FIG. 4C illustrates a 9×9diamond shape filter. Information indicating the filter shape issignalled at the picture level. Note that the signaling of informationindicating the filter shape need not be performed at the picture level,and may be performed at another level (for example, at the sequencelevel, slice level, tile level, CTU level, or CU level).

The enabling or disabling of ALF is determined at the picture level orCU level. For example, for luma, the decision to apply ALF or not isdone at the CU level, and for chroma, the decision to apply ALF or notis done at the picture level. Information indicating whether ALF isenabled or disabled is signalled at the picture level or CU level. Notethat the signaling of information indicating whether ALF is enabled ordisabled need not be performed at the picture level or CU level, and maybe performed at another level (for example, at the sequence level, slicelevel, tile level, or CTU level).

The coefficients set for the plurality of selectable filters (forexample, 15 or 25 filters) is signalled at the picture level. Note thatthe signaling of the coefficients set need not be performed at thepicture level, and may be performed at another level (for example, atthe sequence level, slice level, tile level, CTU level, CU level, orsub-block level).

[Frame Memory]

Frame memory 122 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 122 stores reconstructed blocks filtered byloop filter 120.

[Intra Predictor]

Intra predictor 124 generates a prediction signal (intra predictionsignal) by intra predicting the current block with reference to a blockor blocks in the current picture and stored in block memory 118 (alsoreferred to as intra frame prediction). More specifically, intrapredictor 124 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 128.

For example, intra predictor 124 performs intra prediction by using onemode from among a plurality of predefined intra prediction modes. Theintra prediction modes include one or more non-directional predictionmodes and a plurality of directional prediction modes.

The one or more non-directional prediction modes include, for example,planar prediction mode and DC prediction mode defined in theH.265/high-efficiency video coding (HEVC) standard (see NPL 1).

The plurality of directional prediction modes include, for example, the33 directional prediction modes defined in the H.265/HEVC standard. Notethat the plurality of directional prediction modes may further include32 directional prediction modes in addition to the 33 directionalprediction modes (for a total of 65 directional prediction modes). FIG.5A illustrates 67 intra prediction modes used in intra prediction (twonon-directional prediction modes and 65 directional prediction modes).The solid arrows represent the 33 directions defined in the H.265/HEVCstandard, and the dashed arrows represent the additional 32 directions.

Note that a luma block may be referenced in chroma block intraprediction. In other words, a chroma component of the current block maybe predicted based on a luma component of the current block. Such intraprediction is also referred to as cross-component linear model (CCLM)prediction. Such a chroma block intra prediction mode that references aluma block (referred to as, for example, CCLM mode) may be added as oneof the chroma block intra prediction modes.

Intra predictor 124 may correct post-intra-prediction pixel values basedon horizontal/vertical reference pixel gradients. Intra predictionaccompanied by this sort of correcting is also referred to as positiondependent intra prediction combination (PDPC). Information indicatingwhether to apply PDPC or not (referred to as, for example, a PDPC flag)is, for example, signalled at the CU level. Note that the signaling ofthis information need not be performed at the CU level, and may beperformed at another level (for example, on the sequence level, picturelevel, slice level, tile level, or CTU level).

[Inter Predictor]

Inter predictor 126 generates a prediction signal (inter predictionsignal) by inter predicting the current block with reference to a blockor blocks in a reference picture, which is different from the currentpicture and is stored in frame memory 122 (also referred to as interframe prediction). Inter prediction is performed per current block orper sub-block (for example, per 4×4 block) in the current block. Forexample, inter predictor 126 performs motion estimation in a referencepicture for the current block or sub-block. Inter predictor 126 thengenerates an inter prediction signal of the current block or sub-blockby motion compensation by using motion information (for example, amotion vector) obtained from motion estimation. Inter predictor 126 thenoutputs the generated inter prediction signal to prediction controller128.

The motion information used in motion compensation is signalled. Amotion vector predictor may be used for the signaling of the motionvector. In other words, the difference between the motion vector and themotion vector predictor may be signalled.

Note that the inter prediction signal may be generated using motioninformation for a neighboring block in addition to motion informationfor the current block obtained from motion estimation. Morespecifically, the inter prediction signal may be generated per sub-blockin the current block by calculating a weighted sum of a predictionsignal based on motion information obtained from motion estimation and aprediction signal based on motion information for a neighboring block.Such inter prediction (motion compensation) is also referred to asoverlapped block motion compensation (OBMC).

In such an OBMC mode, information indicating sub-block size for OBMC(referred to as, for example, OBMC block size) is signalled at thesequence level. Moreover, information indicating whether to apply theOBMC mode or not (referred to as, for example, an OBMC flag) issignalled at the CU level. Note that the signaling of such informationneed not be performed at the sequence level and CU level, and may beperformed at another level (for example, at the picture level, slicelevel, tile level, CTU level, or sub-block level).

Hereinafter, the OBMC mode will be described in further detail. FIG. 5Bis a flowchart and FIG. 5C is a conceptual diagram for illustrating anoutline of a prediction image correction process performed via OBMCprocessing.

First, a prediction image (Pred) is obtained through typical motioncompensation using a motion vector (MV) assigned to the current block.

Next, a prediction image (Pred_L) is obtained by applying a motionvector (MV_L) of the encoded neighboring left block to the currentblock, and a first pass of the correction of the prediction image ismade by superimposing the prediction image and Pred_L.

Similarly, a prediction image (Pred_U) is obtained by applying a motionvector (MV_U) of the encoded neighboring upper block to the currentblock, and a second pass of the correction of the prediction image ismade by superimposing the prediction image resulting from the first passand Pred_U. The result of the second pass is the final prediction image.

Note that the above example is of a two-pass correction method using theneighboring left and upper blocks, but the method may be a three-pass orhigher correction method that also uses the neighboring right and/orlower block.

Note that the region subject to superimposition may be the entire pixelregion of the block, and, alternatively, may be a partial block boundaryregion.

Note that here, the prediction image correction process is described asbeing based on a single reference picture, but the same applies when aprediction image is corrected based on a plurality of referencepictures. In such a case, after corrected prediction images resultingfrom performing correction based on each of the reference pictures areobtained, the obtained corrected prediction images are furthersuperimposed to obtain the final prediction image.

Note that the unit of the current block may be a prediction block and,alternatively, may be a sub-block obtained by further dividing theprediction block.

One example of a method for determining whether to implement OBMCprocessing is by using an obmc_flag, which is a signal that indicateswhether to implement OBMC processing. As one specific example, theencoder determines whether the current block belongs to a regionincluding complicated motion. The encoder sets the obmc_flag to a valueof “1” when the block belongs to a region including complicated motionand implements OBMC processing when encoding, and sets the obmc_flag toa value of “0” when the block does not belong to a region includingcomplication motion and encodes without implementing OBMC processing.The decoder switches between implementing OBMC processing or not bydecoding the obmc_flag written in the stream and performing the decodingin accordance with the flag value.

Note that the motion information may be derived on the decoder sidewithout being signalled. For example, a merge mode defined in theH.265/HEVC standard may be used. Moreover, for example, the motioninformation may be derived by performing motion estimation on thedecoder side. In this case, motion estimation is performed without usingthe pixel values of the current block.

Here, a mode for performing motion estimation on the decoder side willbe described. A mode for performing motion estimation on the decoderside is also referred to as pattern matched motion vector derivation(PMMVD) mode or frame rate up-conversion (FRUC) mode.

One example of FRUC processing is illustrated in FIG. 5D. First, acandidate list (a candidate list may be a merge list) of candidates eachincluding a motion vector predictor is generated with reference tomotion vectors of encoded blocks that spatially or temporally neighborthe current block. Next, the best candidate MV is selected from among aplurality of candidate MVs registered in the candidate list. Forexample, evaluation values for the candidates included in the candidatelist are calculated and one candidate is selected based on thecalculated evaluation values.

Next, a motion vector for the current block is derived from the motionvector of the selected candidate. More specifically, for example, themotion vector for the current block is calculated as the motion vectorof the selected candidate (best candidate MV), as-is. Alternatively, themotion vector for the current block may be derived by pattern matchingperformed in the vicinity of a position in a reference picturecorresponding to the motion vector of the selected candidate. In otherwords, when the vicinity of the best candidate MV is searched via thesame method and an MV having a better evaluation value is found, thebest candidate MV may be updated to the MV having the better evaluationvalue, and the MV having the better evaluation value may be used as thefinal MV for the current block. Note that a configuration in which thisprocessing is not implemented is also acceptable.

The same processes may be performed in cases in which the processing isperformed in units of sub-blocks.

Note that an evaluation value is calculated by calculating thedifference in the reconstructed image by pattern matching performedbetween a region in a reference picture corresponding to a motion vectorand a predetermined region. Note that the evaluation value may becalculated by using some other information in addition to thedifference.

The pattern matching used is either first pattern matching or secondpattern matching. First pattern matching and second pattern matching arealso referred to as bilateral matching and template matching,respectively.

In the first pattern matching, pattern matching is performed between twoblocks along the motion trajectory of the current block in two differentreference pictures. Therefore, in the first pattern matching, a regionin another reference picture conforming to the motion trajectory of thecurrent block is used as the predetermined region for theabove-described calculation of the candidate evaluation value.

FIG. 6 is for illustrating one example of pattern matching (bilateralmatching) between two blocks along a motion trajectory. As illustratedin FIG. 6 , in the first pattern matching, two motion vectors (MV0, MV1)are derived by finding the best match between two blocks along themotion trajectory of the current block (Cur block) in two differentreference pictures (Ref0, Ref1). More specifically, a difference between(i) a reconstructed image in a specified position in a first encodedreference picture (Ref0) specified by a candidate MV and (ii) areconstructed picture in a specified position in a second encodedreference picture (Ref1) specified by a symmetrical MV scaled at adisplay time interval of the candidate MV may be derived, and theevaluation value for the current block may be calculated by using thederived difference. The candidate MV having the best evaluation valueamong the plurality of candidate MVs may be selected as the final MV.

Under the assumption of continuous motion trajectory, the motion vectors(MV0, MV1) pointing to the two reference blocks shall be proportional tothe temporal distances (TD0, TD1) between the current picture (Cur Pic)and the two reference pictures (Ref0, Ref1). For example, when thecurrent picture is temporally between the two reference pictures and thetemporal distance from the current picture to the two reference picturesis the same, the first pattern matching derives a mirror basedbi-directional motion vector.

In the second pattern matching, pattern matching is performed between atemplate in the current picture (blocks neighboring the current block inthe current picture (for example, the top and/or left neighboringblocks)) and a block in a reference picture. Therefore, in the secondpattern matching, a block neighboring the current block in the currentpicture is used as the predetermined region for the above-describedcalculation of the candidate evaluation value.

FIG. 7 is for illustrating one example of pattern matching (templatematching) between a template in the current picture and a block in areference picture. As illustrated in FIG. 7 , in the second patternmatching, a motion vector of the current block is derived by searching areference picture (Ref0) to find the block that best matches neighboringblocks of the current block (Cur block) in the current picture (CurPic). More specifically, a difference between (i) a reconstructed imageof an encoded region that is both or one of the neighboring left andneighboring upper region and (ii) a reconstructed picture in the sameposition in an encoded reference picture (Ref0) specified by a candidateMV may be derived, and the evaluation value for the current block may becalculated by using the derived difference. The candidate MV having thebest evaluation value among the plurality of candidate MVs may beselected as the best candidate MV.

Information indicating whether to apply the FRUC mode or not (referredto as, for example, a FRUC flag) is signalled at the CU level. Moreover,when the FRUC mode is applied (for example, when the FRUC flag is set totrue), information indicating the pattern matching method (first patternmatching or second pattern matching) is signalled at the CU level. Notethat the signaling of such information need not be performed at the CUlevel, and may be performed at another level (for example, at thesequence level, picture level, slice level, tile level, CTU level, orsub-block level).

Here, a mode for deriving a motion vector based on a model assuminguniform linear motion will be described. This mode is also referred toas a bi-directional optical flow (BIO) mode.

FIG. 8 is for illustrating a model assuming uniform linear motion. InFIG. 8 , (v_(x), v_(y)) denotes a velocity vector, and τ₀ and τ₁ denotetemporal distances between the current picture (Cur Pic) and tworeference pictures (Ref₀, Ref₁). (MVx₀, MVy₀) denotes a motion vectorcorresponding to reference picture Ref₀, and (MVx₁, MVy₁) denotes amotion vector corresponding to reference picture Ref₁.

Here, under the assumption of uniform linear motion exhibited byvelocity vector (v_(x), v_(y)), (MVx₀, MVy₀) and (MVx₁, MVy₁) arerepresented as (v_(x)τ₀, v_(y)τ₀) and (−v_(x)τ₁, −v_(y)τ₁),respectively, and the following optical flow equation is given.

MATH. 1

∂I ^((k)) /∂t+v _(x) ∂I ^((k)) /∂x+v _(y) ∂I ^((k)) /∂y=0.  (1)

Here, I^((k)) denotes a luma value from reference picture k (k=0, 1)after motion compensation. This optical flow equation shows that the sumof (i) the time derivative of the luma value, (ii) the product of thehorizontal velocity and the horizontal component of the spatial gradientof a reference picture, and (iii) the product of the vertical velocityand the vertical component of the spatial gradient of a referencepicture is equal to zero. A motion vector of each block obtained from,for example, a merge list is corrected pixel by pixel based on acombination of the optical flow equation and Hermite interpolation.

Note that a motion vector may be derived on the decoder side using amethod other than deriving a motion vector based on a model assuminguniform linear motion. For example, a motion vector may be derived foreach sub-block based on motion vectors of neighboring blocks.

Here, a mode in which a motion vector is derived for each sub-blockbased on motion vectors of neighboring blocks will be described. Thismode is also referred to as affine motion compensation prediction mode.

FIG. 9A is for illustrating deriving a motion vector of each sub-blockbased on motion vectors of neighboring blocks. In FIG. 9A, the currentblock includes 16 4×4 sub-blocks. Here, motion vector v₀ of the top leftcorner control point in the current block is derived based on motionvectors of neighboring sub-blocks, and motion vector v₁ of the top rightcorner control point in the current block is derived based on motionvectors of neighboring blocks. Then, using the two motion vectors v₀ andv₁, the motion vector (v_(x), v_(y)) of each sub-block in the currentblock is derived using Equation 2 below.

$\begin{matrix}{{MATH}.2} &  \\\left\{ \begin{matrix}{v_{x} = {{\frac{\left( {v_{1x} - v_{0x}} \right)}{w}x} - {\frac{\left( {v_{1y} - v_{0y}} \right)}{w}y} + v_{0x}}} \\{v_{y} = {{\frac{\left( {v_{1y} - v_{0y}} \right)}{w}x} + {\frac{\left( {v_{1x} - v_{0x}} \right)}{w}y} + v_{0y}}}\end{matrix} \right. & (2)\end{matrix}$

Here, x and y are the horizontal and vertical positions of thesub-block, respectively, and w is a predetermined weighted coefficient.

Such an affine motion compensation prediction mode may include a numberof modes of different methods of deriving the motion vectors of the topleft and top right corner control points. Information indicating such anaffine motion compensation prediction mode (referred to as, for example,an affine flag) is signalled at the CU level. Note that the signaling ofinformation indicating the affine motion compensation prediction modeneed not be performed at the CU level, and may be performed at anotherlevel (for example, at the sequence level, picture level, slice level,tile level, CTU level, or sub-block level).

[Prediction Controller]

Prediction controller 128 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto subtractor 104 and adder 116.

Here, an example of deriving a motion vector via merge mode in a currentpicture will be given. FIG. 9B is for illustrating an outline of aprocess for deriving a motion vector via merge mode.

First, an MV predictor list in which candidate MV predictors areregistered is generated. Examples of candidate MV predictors include:spatially neighboring MV predictors, which are MVs of encoded blockspositioned in the spatial vicinity of the current block; a temporallyneighboring MV predictor, which is an MV of a block in an encodedreference picture that neighbors a block in the same location as thecurrent block; a combined MV predictor, which is an MV generated bycombining the MV values of the spatially neighboring MV predictor andthe temporally neighboring MV predictor; and a zero MV predictor, whichis an MV whose value is zero.

Next, the MV of the current block is determined by selecting one MVpredictor from among the plurality of MV predictors registered in the MVpredictor list.

Furthermore, in the variable-length encoder, a merge_idx, which is asignal indicating which MV predictor is selected, is written and encodedinto the stream.

Note that the MV predictors registered in the MV predictor listillustrated in FIG. 9B constitute one example. The number of MVpredictors registered in the MV predictor list may be different from thenumber illustrated in FIG. 9B, the MV predictors registered in the MVpredictor list may omit one or more of the types of MV predictors givenin the example in FIG. 9B, and the MV predictors registered in the MVpredictor list may include one or more types of MV predictors inaddition to and different from the types given in the example in FIG.9B.

Note that the final MV may be determined by performing DMVR processing(to be described later) by using the MV of the current block derived viamerge mode.

Here, an example of determining an MV by using DMVR processing will begiven.

FIG. 9C is a conceptual diagram for illustrating an outline of DMVRprocessing.

First, the most appropriate MVP set for the current block is consideredto be the candidate MV, reference pixels are obtained from a firstreference picture, which is a picture processed in the L0 direction inaccordance with the candidate MV, and a second reference picture, whichis a picture processed in the L1 direction in accordance with thecandidate MV, and a template is generated by calculating the average ofthe reference pixels.

Next, using the template, the surrounding regions of the candidate MVsof the first and second reference pictures are searched, and the MV withthe lowest cost is determined to be the final MV Note that the costvalue is calculated using, for example, the difference between eachpixel value in the template and each pixel value in the regionssearched, as well as the MV value.

Note that the outlines of the processes described here are fundamentallythe same in both the encoder and the decoder.

Note that processing other than the processing exactly as describedabove may be used, so long as the processing is capable of deriving thefinal MV by searching the surroundings of the candidate MV.

Here, an example of a mode that generates a prediction image by usingLIC processing will be given.

FIG. 9D is for illustrating an outline of a prediction image generationmethod using a luminance correction process performed via LICprocessing.

First, an MV is extracted for obtaining, from an encoded referencepicture, a reference image corresponding to the current block.

Next, information indicating how the luminance value changed between thereference picture and the current picture is extracted and a luminancecorrection parameter is calculated by using the luminance pixel valuesfor the encoded left neighboring reference region and the encoded upperneighboring reference region, and the luminance pixel value in the samelocation in the reference picture specified by the MV.

The prediction image for the current block is generated by performing aluminance correction process by using the luminance correction parameteron the reference image in the reference picture specified by the MV.

Note that the shape of the surrounding reference region illustrated inFIG. 9D is just one example; the surrounding reference region may have adifferent shape.

Moreover, although a prediction image is generated from a singlereference picture in this example, in cases in which a prediction imageis generated from a plurality of reference pictures as well, theprediction image is generated after performing a luminance correctionprocess, via the same method, on the reference images obtained from thereference pictures.

One example of a method for determining whether to implement LICprocessing is by using an lic_flag, which is a signal that indicateswhether to implement LIC processing. As one specific example, theencoder determines whether the current block belongs to a region ofluminance change. The encoder sets the lic_flag to a value of “1” whenthe block belongs to a region of luminance change and implements LICprocessing when encoding, and sets the lic_flag to a value of “0” whenthe block does not belong to a region of luminance change and encodeswithout implementing LIC processing. The decoder switches betweenimplementing LIC processing or not by decoding the lic_flag written inthe stream and performing the decoding in accordance with the flagvalue.

One example of a different method of determining whether to implementLIC processing is determining so in accordance with whether LICprocessing was determined to be implemented for a surrounding block. Inone specific example, when merge mode is used on the current block,whether LIC processing was applied in the encoding of the surroundingencoded block selected upon deriving the MV in the merge mode processingmay be determined, and whether to implement LIC processing or not can beswitched based on the result of the determination. Note that in thisexample, the same applies to the processing performed on the decoderside.

[Decoder Outline]

Next, a decoder capable of decoding an encoded signal (encodedbitstream) output from encoder 100 will be described. FIG. 10 is a blockdiagram illustrating a functional configuration of decoder 200 accordingto Embodiment 1. Decoder 200 is a moving picture/picture decoder thatdecodes a moving picture/picture block by block.

As illustrated in FIG. 10 , decoder 200 includes entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, block memory210, loop filter 212, frame memory 214, intra predictor 216, interpredictor 218, and prediction controller 220.

Decoder 200 is realized as, for example, a generic processor and memory.In this case, when a software program stored in the memory is executedby the processor, the processor functions as entropy decoder 202,inverse quantizer 204, inverse transformer 206, adder 208, loop filter212, intra predictor 216, inter predictor 218, and prediction controller220. Alternatively, decoder 200 may be realized as one or more dedicatedelectronic circuits corresponding to entropy decoder 202, inversequantizer 204, inverse transformer 206, adder 208, loop filter 212,intra predictor 216, inter predictor 218, and prediction controller 220.

Hereinafter, each component included in decoder 200 will be described.

[Entropy Decoder]

Entropy decoder 202 entropy decodes an encoded bitstream. Morespecifically, for example, entropy decoder 202 arithmetic decodes anencoded bitstream into a binary signal. Entropy decoder 202 thendebinarizes the binary signal. With this, entropy decoder 202 outputsquantized coefficients of each block to inverse quantizer 204.

[Inverse Quantizer]

Inverse quantizer 204 inverse quantizes quantized coefficients of ablock to be decoded (hereinafter referred to as a current block), whichare inputs from entropy decoder 202. More specifically, inversequantizer 204 inverse quantizes quantized coefficients of the currentblock based on quantization parameters corresponding to the quantizedcoefficients. Inverse quantizer 204 then outputs the inverse quantizedcoefficients (i.e., transform coefficients) of the current block toinverse transformer 206.

[Inverse Transformer]

Inverse transformer 206 restores prediction errors by inversetransforming transform coefficients, which are inputs from inversequantizer 204.

For example, when information parsed from an encoded bitstream indicatesapplication of EMT or AMT (for example, when the AMT flag is set totrue), inverse transformer 206 inverse transforms the transformcoefficients of the current block based on information indicating theparsed transform type.

Moreover, for example, when information parsed from an encoded bitstreamindicates application of NSST, inverse transformer 206 applies asecondary inverse transform to the transform coefficients.

[Adder]

Adder 208 reconstructs the current block by summing prediction errors,which are inputs from inverse transformer 206, and prediction samples,which is an input from prediction controller 220. Adder 208 then outputsthe reconstructed block to block memory 210 and loop filter 212.

[Block Memory]

Block memory 210 is storage for storing blocks in a picture to bedecoded (hereinafter referred to as a current picture) for reference inintra prediction. More specifically, block memory 210 storesreconstructed blocks output from adder 208.

[Loop Filter]

Loop filter 212 applies a loop filter to blocks reconstructed by adder208, and outputs the filtered reconstructed blocks to frame memory 214and, for example, a display device.

When information indicating the enabling or disabling of ALF parsed froman encoded bitstream indicates enabled, one filter from among aplurality of filters is selected based on direction and activity oflocal gradients, and the selected filter is applied to the reconstructedblock.

[Frame Memory]

Frame memory 214 is storage for storing reference pictures used in interprediction, and is also referred to as a frame buffer. Morespecifically, frame memory 214 stores reconstructed blocks filtered byloop filter 212.

[Intra Predictor]

Intra predictor 216 generates a prediction signal (intra predictionsignal) by intra prediction with reference to a block or blocks in thecurrent picture and stored in block memory 210. More specifically, intrapredictor 216 generates an intra prediction signal by intra predictionwith reference to samples (for example, luma and/or chroma values) of ablock or blocks neighboring the current block, and then outputs theintra prediction signal to prediction controller 220.

Note that when an intra prediction mode in which a chroma block is intrapredicted from a luma block is selected, intra predictor 216 may predictthe chroma component of the current block based on the luma component ofthe current block.

Moreover, when information indicating the application of PDPC is parsedfrom an encoded bitstream, intra predictor 216 correctspost-intra-prediction pixel values based on horizontal/verticalreference pixel gradients.

[Inter Predictor]

Inter predictor 218 predicts the current block with reference to areference picture stored in frame memory 214. Inter prediction isperformed per current block or per sub-block (for example, per 4×4block) in the current block. For example, inter predictor 218 generatesan inter prediction signal of the current block or sub-block by motioncompensation by using motion information (for example, a motion vector)parsed from an encoded bitstream, and outputs the inter predictionsignal to prediction controller 220.

Note that when the information parsed from the encoded bitstreamindicates application of OBMC mode, inter predictor 218 generates theinter prediction signal using motion information for a neighboring blockin addition to motion information for the current block obtained frommotion estimation.

Moreover, when the information parsed from the encoded bitstreamindicates application of FRUC mode, inter predictor 218 derives motioninformation by performing motion estimation in accordance with thepattern matching method (bilateral matching or template matching) parsedfrom the encoded bitstream. Inter predictor 218 then performs motioncompensation using the derived motion information.

Moreover, when BIO mode is to be applied, inter predictor 218 derives amotion vector based on a model assuming uniform linear motion. Moreover,when the information parsed from the encoded bitstream indicates thataffine motion compensation prediction mode is to be applied, interpredictor 218 derives a motion vector of each sub-block based on motionvectors of neighboring blocks.

[Prediction Controller]

Prediction controller 220 selects either the intra prediction signal orthe inter prediction signal, and outputs the selected prediction signalto adder 208.

[Details of Inter Prediction]

Next, the details of inter prediction will be described.

For example, in encoder 100, inter predictor 126 determines which modeis used to perform the prediction process, among a plurality of modesincluding a first mode in which the prediction process is performedbased on a motion vector of each block in a video and a second mode inwhich the prediction process is performed based on a motion vector ofeach sub-block obtained by splitting the block. Subsequently, when theprediction process is performed in the first mode, inter predictor 126determines whether to perform a correction process on a prediction imageusing a spatial gradient of pixel values in the prediction imageobtained by performing the prediction process, and performs thecorrection process when it is determined to perform the correctionprocess. On the other hand, when the prediction process is performed inthe second mode, inter predictor 126 does not perform the correctionprocess.

Subsequently, based on the above prediction process, inter predictor 126derives a prediction sample set for a current CU to be encoded. Afterthis, subtractor 104, transformer 106, quantizer 108, entropy encoder110, and so on encode the current CU using the prediction sample set.

Furthermore, the inter prediction in decoder 200 is the same as theinter prediction in encoder 100. For example, in decoder 200, interpredictor 218 determines which mode is used to perform the predictionprocess, among a plurality of modes including a first mode in which theprediction process is performed based on a motion vector of each blockin a video and a second mode in which the prediction process isperformed based on a motion vector of each sub-block obtained bysplitting the block. Subsequently, when the prediction process isperformed in the first mode, inter predictor 128 determines whether toperform a correction process on a prediction image using a spatialgradient of pixel values in the prediction image obtained by performingthe prediction process, and performs the correction process when it isdetermined to perform the correction process. On the other hand, whenthe prediction process is performed in the second mode, inter predictor128 does not perform the correction process. Note that, in decoder 200,when the prediction process is performed in the first mode, interpredictor 218 determines whether to perform a correction process, basedon determination result information indicating a result of thedetermining whether to perform the correction process on the predictionimage using the spatial gradient of pixel values in the prediction imageobtained by performing the prediction process in encoder 100.

Subsequently, based on the above prediction process, inter predictor 218derives a prediction sample set for a current CU to be encoded. Afterthis, entropy decoder 202, inverse quantizer 204, inverse transformer206, adder 208, and so on decode the current CU using the predictionsample set.

The following more specifically describes the details of interprediction.

FIG. 11 is a flow chart for illustrating one example of the operationperformed by encoder 100 and decoder 200 according to the primaryaspect.

Hereinafter, the operation performed by encoder 100 will be described,but the operation performed by decoder 200 is the same as the operationperformed by encoder 100. Furthermore, processes related to the interprediction are mainly performed by inter predictor 126 in encoder 100,and by inter predictor 218 in decoder 200.

As shown in FIG. 11 , the operation of inter predictor 126 in theencoder according to the primary aspect is characterized by theoperation in merge mode. The inter prediction has a mode in whichcandidate MVs for a current CU to be encoded are generated for each CU(i.e., the first mode), and a mode in which candidate MVs are generatedfor each sub-CU obtained by splitting a CU into N×N blocks (i.e., thesecond mode). In the mode in which the candidate MVs are generated foreach sub-CU (the second mode), after the motion prediction is performedfor each sub-CU, a per-pixel motion prediction is not performed. Inother words, in the second mode, a MV is derived for each sub-block, andafter the motion compensation (MC processing) is performed for eachsub-block using the derived MV to generate a prediction image, theprediction image is not corrected on a per-pixel basis. Accordingly,when a current CU to be encoded is encoded in the second mode,determination result information (referred to as a flag, for example)need not be encoded indicating whether to perform the per-pixel motioncorrection in the prediction image.

On the other hand, in the mode in which the candidate MVs are generatedfor each CU (the first mode), after the motion prediction is performedfor each CU, the per-pixel motion prediction is performed to correct theresult of the motion prediction for each CU on a per-pixel basis. Inother words, in the first mode, the MV is derived for each block, andafter the motion compensation (MC processing) is performed for eachblock using the derived MV to generate a prediction image, theprediction image is corrected using a spatial gradient of pixel valuesin the prediction image. Here, whether to perform the per-pixel motionprediction may be an optional configuration. Accordingly, when a currentCU to be encoded is encoded in the first mode, a flag may be encodedindicating whether to perform the per-pixel motion correction in theprediction image. Furthermore, the CU may be a non-square of M×N, etc.,and the sub-CU may be a unit obtained by splitting a CU into any shapes.For example, a method such as bi-directional optical flow (BIO) can beused as the per-pixel motion correction. Note that the per-pixel motioncorrection may be performed for each pixel, or for each of sets ofpixels. For example, a set of pixels may be a block or a sub-block.

Due to the combination with the motion prediction for each CU, theper-pixel motion prediction has large coding-efficiency enhancingeffects. The motion prediction for each sub-block has a greater amountof processing than the motion prediction for each CU. In the interprediction of encoder 100 according to the primary aspect, the per-pixelmotion prediction is allowed only for the motion prediction for each CU,and thereby it is possible to reduce the amount of processing of themerge mode while maintaining the coding efficiency.

Referring to FIG. 11 , an operation example of encoder 100 will be morespecifically described below.

When the motion prediction is performed without using the merge mode (Noat S100), encoder 100 performs the motion prediction using apredetermined mode different from the merge mode (S105). The modedifferent from the merge mode may be, for example, a normal inter modein which a difference between a MV predictor and a MV is derived.

On the other hand, when the motion prediction is performed using themerge mode (Yes at S100) and candidate MVs are generated for each sub-CU(Yes at S101), encoder 100 performs the motion prediction for eachsub-CU based on the candidate MVs for each sub-CU (S102).

Furthermore, when the motion prediction is performed using the mergemode (Yes at S100) and candidate MVs are not generated for each sub-CU(No at S101), encoder 100 performs the motion prediction for each CUbased on the candidate MVs for each CU (S103). Subsequently, encoder 100determines whether to perform the per-pixel motion correction (notshown). When it is determined to perform the per-pixel motion correction(not shown), encoder 100 performs the per-pixel motion correction(S104). On the other hand, when it is determined not to perform theper-pixel motion correction (not shown), encoder 100 does not performthe per-pixel motion correction (not shown). Note that encoder 100 mayencode the determination result information indicating whether toperform the per-pixel motion correction.

FIG. 12 is a flow chart for illustrating one example of the operationperformed by encoder 100 and decoder 200 according to the primaryaspect. FIG. 11 illustrates a method for enabling and disabling theper-pixel motion prediction in the merge mode, but the presentdisclosure is not limited to the merge mode. For example, as shown inthe operation flow of FIG. 12 , encoder 100 may enable and disable theper-pixel motion prediction. Furthermore, in FRUC, when the motionestimation is performed only for each CU, encoder 100 may enable theper-pixel motion prediction, whereas when the motion estimation isfurther performed for each sub-CU, encoder 100 may disable the per-pixelmotion prediction. Furthermore, after performing the motion predictionfor each sub-CU, motion prediction having a lower amount of processingthan the per-pixel motion prediction following the motion prediction foreach CU may be performed to correct the motion in the prediction image.

As shown in FIG. 12 , encoder 100 determines whether to generatecandidate MVs for each sub-CU (S101). When it is determined to generatecandidate MVs for each sub-CU (Yes at S101), encoder 100 performs themotion prediction for each sub-CU based on the candidate MVs for eachsub-CU (S102). For example, a method based on the merge mode, a methodbased on the affine mode, etc., are listed as the methods for performingthe motion prediction for each sub-CU. Furthermore, the merge modeincludes ATMVP mode and STMVP mode. ATMVP mode and STMVP mode will bedescribed below in detail.

On the other hand, when it is determined not to generate candidate MVsfor each sub-CU (No at S101), encoder 100 performs the motion predictionfor each CU based on candidate MVs for each CU (S103). For example, amethod based on the normal inter mode, a method based on the merge mode,a method based on the affine mode, etc., are listed as the methods forperforming the motion prediction for each CU.

Subsequently, encoder 100 determines whether to perform the per-pixelmotion correction (not shown). When it is determined to perform theper-pixel motion correction (not shown), encoder 100 performs theper-pixel motion correction (S104). On the other hand, when it isdetermined not to perform the per-pixel motion correction (not shown),encoder 100 does not perform the per-pixel motion correction (notshown). Note that encoder 100 may encode the determination resultinformation indicating whether to perform the per-pixel motioncorrection.

The foregoing has described an operation example of the encoding method.Decoding also has the same operation, and the per-pixel motioncorrection is not performed when the motion prediction is performed foreach sub-CU based on the candidate MVs for each sub-CU. In other words,when the candidate MVs are generated for each CU (i.e., in the firstmode), the motion correction (i.e., the correction process) is allowed,whereas when the candidate MVs are generated for each sub-CU (i.e., inthe second mode), the motion correction (i.e., the correction process)is prevented. When the candidate MVs are generated for each CU, decoder200 determines whether to perform the per-pixel motion correction, basedon the determination result information generated by encoder 100. Notethat decoder 200 may decode the determination result informationindicating whether to perform the per-pixel motion correction.

The following describes a method for determining a sub-CU MV (a motionvector of each sub-block) in ATMVP mode and STMVP mode, which are eachlisted as an example of the mode in which a MV is determined for eachsub-CU. Note that, as described above, ATMVP mode and STMVP mode areincluded in the merge mode in which a motion vector predictor is used asa motion vector. In the merge mode, one candidate MV is selected from aMV candidate list generated with reference to the encoded blocks todetermine the MV of the current block. ATMVP mode and STMVP mode arelisted as a mode for registration on the MV candidate list.

FIG. 13 is a diagram illustrating one example of a method fordetermining a motion vector of each sub-block in ATMVP mode. Firstly, atemporal MV for a current CU to be encoded (the current CU in FIG. 13 )is selected from among MVs of the CUs neighboring the current CU. Thetemporal MV can be selected from blocks which are merge candidates. Forexample, search is performed on the merge candidates in order ofincreasing index number, and the MV of the available merge candidateblock is determined as the temporal MV of the current CU. Subsequently,the position of the reference CU in the reference picture is determinedbased on the temporal MV, and the sub-CU MV in the reference CU isobtained. Then, the obtained sub-CU MV in the reference CU is used asthe MV of the corresponding sub-CU in the current CU (hereinafter, alsoreferred to as a sub-CU MV of the current CU). When a sub-CU in thereference CU has multiple MVs (L0, L1) and the pictures to be referredto can be obtained, the MVs (L0, L1) are each used as the sub-CU MV ofthe current CU. The process in encoding has been described here.Decoding also has the same process.

FIG. 14 is a diagram illustrating one example of a method fordetermining a motion vector of each sub-block in STMVP mode. In STMVPmode, the sub-block motion vector is determined by for example, for eachsub-CU, averaging or weighted adding the MVs of spatially neighboringN×N blocks and the MV obtained from a temporally different referencepicture. More specifically, in STMVP mode, firstly, a temporal-MVreference block co-located with the current block is identified in theencoded reference picture. Subsequently, for each of the sub-blocks inthe current block, the MV of the spatially neighboring upper sub-block,the MV of the spatially neighboring left sub-block, and the MV used inthe encoding of the temporal-MV reference block are identified. Then,the average of the values obtained by scaling the identified MVs basedon the time interval is calculated to obtain the MV of each sub-block.

In the example of FIG. 14 , with respect to the sub-CU of A, the spatialMVs and the temporal MV are determined based on the MVs of the spatiallyneighboring upper block (c or d) and the spatially neighboring leftblock (b or a) and based on the MV of the N×N block in the referencepicture co-located with the sub-CU of D, respectively, and the spatialMVs and the temporal MV are averaged to determine the resultant as theMV of the sub-CU of A. Here, with respect to the sub-CUs of B, C, D,etc., the MV of the encoded or decoded sub-CU can be used to determinethe spatial MV For example, with respect to the sub-CU of B, the sub-CUof A can be used as the spatially neighboring left block. The process inencoding has been described here. Decoding also has the same process.

Implementation Example

FIG. 15 is a block diagram illustrating an implementation example ofencoder 100. Encoder 100 includes circuitry 160 and memory 162. Forexample, the components in encoder 100 shown in FIG. 1 are implementedas circuitry 160 and memory 162 shown in FIG. 15 .

Circuitry 160 is an electronic circuit accessible to memory 162, andperforms information processing. For example, circuitry 160 is adedicated or general-purpose electronic circuit for encoding a videousing memory 162. Circuitry 160 may be a processor such as a CPU.Circuitry 160 also may be an assembly of electronic circuits.

Furthermore, for example, circuitry 160 may serve as some componentsother than components for storing information, among the components inencoder 100 shown in FIG. 1 . In other words, circuitry 160 may performthe foregoing operation as the operation of these components.

Memory 162 is a dedicated or general-purpose memory that storesinformation for encoding a video in circuitry 160. Memory 162 may be anelectronic circuit which is connected to circuitry 160, or included incircuitry 160.

Memory 162 also may be an assembly of electronic circuits, or may becomposed of multiple sub-memories. Memory 162 also may be a magneticdisk, an optical disk, etc., and be referred to as a storage, arecording medium, etc. Memory 162 also may be a non-volatile memory or avolatile memory.

Furthermore, for example, memory 162 may serve as components for storinginformation, among the components in encoder 100 shown in FIG. 1 , etc.In particular, memory 162 may serve as block memory 118 and frame memory122 shown in FIG. 1 .

For example, memory 162 may store a video to be encoded, or a bitstreamcorresponding to the encoded video. Memory 162 also may store a programfor encoding a video in circuitry 160.

Note that in encoder 100, all the components shown in FIG. 1 etc., neednot be implemented, or all the foregoing processes need not beperformed. Some of the components shown in FIG. 1 may be included inanother device, or some of the foregoing processes may be performed byanother device. Then, in encoder 100, some of the components shown inFIG. 1 are implemented and some of the forging processes are performed,and thereby it is possible to perform a further subdivided predictionprocess while preventing an increase in the amount of processing.

FIG. 16 is a flow chart for illustrating the operation example ofencoder 100 shown in FIG. 15 . For example, in encoding a video, encoder100 shown in FIG. 15 performs the operation shown in FIG. 16 . Morespecifically, using memory 162, circuitry 160 operates as follows.

Firstly, circuitry 160 determines which mode is used to perform aprediction process, among a plurality of modes including a first mode inwhich the prediction process is performed based on a motion vector ofeach block in a video and a second mode in which the prediction processis performed based on a motion vector of each sub-block obtained bysplitting the block (S201).

Subsequently, when the prediction process is performed in the firstmode, circuitry 160 determines whether to perform a correction processon a prediction image using a spatial gradient of pixel values in theprediction image obtained by performing the prediction process, andperforms the correction process when it is determined to perform thecorrection process (S202). When the prediction process is performed inthe second mode, circuitry 160 does not perform the correction process(S203).

With this, encoder 100 uses a per-subdivided-unit (e.g., per-pixel)motion correction in combination with the motion prediction for eachblock, and thus the coding efficiency is improved. Furthermore, themotion prediction for each sub-block has a greater amount of processingthan the motion prediction for each block, and thus when the motionprediction is performed for each sub-block, the encoder does not performthe per-subdivided-unit motion correction. Thus, the encoder performsthe per-subdivided-unit motion prediction only for the motion predictionfor each block, and thereby it is possible to reduce the amount ofprocessing while maintaining the coding efficiency. Accordingly, theencoder can perform a further subdivided prediction process whilepreventing an increase in the amount of processing.

For example, the first mode and the second mode are included in a mergemode in which a motion vector predictor is used as a motion vector.

With this, encoder 100 can speed up a process for deriving theprediction sample set in the merge mode.

Furthermore, for example, circuitry 160: when the prediction process isperformed in the first mode, encodes determination result informationindicating a result of the determining whether to perform the correctionprocess; and when the prediction process is performed in the secondmode, does not encode the determination result information. With this,encoder 100 can reduce the encoded amount.

Furthermore, for example, the correction process may be a bi-directionaloptical flow (BIO) process. With this, encoder 100 can correct theprediction image using a per-subdivided-unit correction value in theprediction image generated by deriving the motion vector for each block.

Furthermore, for example, the second mode may be an advanced temporalmotion vector prediction (ATMVP) mode. With this, encoder 100 need notperform the per-subdivided-unit motion correction in ATMVP mode, andthus the amount of processing is reduced.

Furthermore, for example, the second mode may be a spatial-temporalmotion vector prediction (STMVP) mode. With this, encoder 100 need notperform the per-subdivided-unit motion correction in STMVP mode, andthus the amount of processing is reduced.

Furthermore, for example, the second mode may be an affine motioncompensation prediction mode. With this, encoder 100 need not performthe per-subdivided-unit motion correction in affine mode, and thus theamount of processing is reduced.

FIG. 17 is a block diagram illustrating an implementation example ofdecoder 200. Decoder 200 includes circuitry 260 and memory 262. Forexample, the components in decoder 200 shown in FIG. 10 are implementedas circuitry 260 and memory 262 shown in FIG. 17 .

Circuitry 260 is an electronic circuit accessible to memory 262, andperforms information processing. For example, circuitry 260 is adedicated or general-purpose electronic circuit for decoding a videousing memory 262. Circuitry 260 may be a processor such as a CPU.Circuitry 260 also may be an assembly of electronic circuits.

Furthermore, for example, circuitry 260 may serve as some componentsother than components for storing information, among the components indecoder 200 shown in FIG. 10 . In other words, circuitry 260 may performthe foregoing operation as the operation of these components.

Memory 262 is a dedicated or general-purpose memory that storesinformation for decoding a video in circuitry 260. Memory 262 may be anelectronic circuit which is connected to circuitry 260, or included incircuitry 260.

Memory 262 also may be an assembly of electronic circuits, or may becomposed of multiple sub-memories. Memory 262 also may be a magneticdisk, an optical disk, etc., and be referred to as a storage, arecording medium, etc. Memory 262 also may be a non-volatile memory or avolatile memory.

For example, memory 262 may serve as components for storing information,among the components in decoder 200 shown in FIG. 10 . In particular,memory 262 may serve as block memory 210 and frame memory 214 shown inFIG. 10 .

Furthermore, memory 262 may store a decoded video, or a bitstreamcorresponding to the encoded video. Memory 262 also may store a programfor decoding a video in circuitry 260.

Note that in decoder 200, all the components shown in FIG. 10 need notbe implemented, or all the foregoing processes need not be performed.Some of the components shown in FIG. 10 may be included in anotherdevice, or some of the foregoing processes may be performed by anotherdevice. Then, in decoder 200, some of the components shown in FIG. 10are implemented and some of the forging processes are performed, andthereby it is possible to perform a further subdivided predictionprocess while preventing an increase in the amount of processing.

FIG. 18 is a flow chart for illustrating the operation example ofdecoder 200 shown in FIG. 17 . For example, in decoding a video, decoder200 shown in FIG. 17 performs the operation shown in FIG. 18 . Morespecifically, using memory 262, circuitry 260 operates as follows.

Firstly, circuitry 260: determines which mode is used to perform theprediction process, among a plurality of modes including a first mode inwhich the prediction process is performed based on a motion vector ofeach block in the video and a second mode in which the predictionprocess is performed based on a motion vector of each sub-block obtainedby splitting the block (S301).

Subsequently, when the prediction process is performed in the firstmode, circuitry 260 determines whether to perform a correction processon a prediction image using a spatial gradient of pixel values in theprediction image obtained by performing the prediction process, andperforms the correction process when it is determined to perform thecorrection process (S302). When the prediction process is performed inthe second mode, circuitry 260 does not perform the correction process(S303).

With this, decoder 200 uses a per-subdivided-unit (e.g., per-pixel)motion correction in combination with the motion prediction for eachblock, and thus the coding efficiency is improved. Furthermore, themotion prediction for each sub-block has a greater amount of processingthan the motion prediction for each block, and thus when the motionprediction is performed for each sub-block, the decoder does not performthe per-subdivided-unit motion correction. Thus, the decoder performsthe per-subdivided-unit motion prediction only for the motion predictionfor each block, and thereby it is possible to reduce the amount ofprocessing while maintaining the coding efficiency. Accordingly, thedecoder can perform a further subdivided prediction process whilepreventing an increase in the amount of processing.

For example, the first mode and the second mode are included in a mergemode in which a motion vector predictor is used as a motion vector.

With this, decoder 200 can speed up a process for deriving theprediction sample set in the merge mode.

Furthermore, for example, the circuitry: when the prediction process isperformed in the first mode, decodes determination result informationindicating a result of the determining whether to perform the correctionprocess; and when the prediction process is performed in the secondmode, does not decode the determination result information. With this,decoder 200 can improve the processing efficiency.

Furthermore, for example, the correction process may be a BIO process.With this, decoder 200 can correct the prediction image using aper-subdivided-unit correction value in the prediction image generatedby deriving the motion vector for each block.

Furthermore, for example, the second mode may be an ATMVP mode. Withthis, decoder 200 need not perform the per-subdivided-unit motioncorrection in ATMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be a STMVP mode. Withthis, decoder 200 need not perform the per-subdivided-unit motioncorrection in STMVP mode, and thus the amount of processing is reduced.

Furthermore, for example, the second mode may be an affine motioncompensation prediction mode. With this, decoder 200 need not performthe per-subdivided-unit motion correction in affine mode, and thus theamount of processing is reduced.

Furthermore, encoder 100 and decoder 200 according to the presentembodiment may be used as an image encoder and an image decoder, or maybe used as a video encoder or a video decoder, respectively.

Alternatively, encoder 100 and decoder 200 are each applicable as aprediction device or an inter prediction device. In other words, encoder100 and decoder 200 may correspond to only inter predictor 126 and interpredictor 218, respectively. The remaining components such as entropyencoder 110, entropy decoder 202, etc., may be included in anotherdevice.

Furthermore, at least part of the present embodiment may be used as anencoding method, a decoding method, a prediction method, or anothermethod.

Furthermore, in the present embodiment, each component may be configuredby a dedicated hardware, or may be implemented by executing a softwareprogram suitable for each component. Each component may be implementedby causing a program executer such as a CPU or a processor to read outand execute a software program stored on a recording medium such as ahard disk or a semiconductor memory.

In particular, encoder 100 and decoder 200 may each include processingcircuitry and a storage which is electrically connected to thisprocessing circuitry and accessible from this processing circuitry. Forexample, the processing circuitry correspond to circuitry 160 or 260,and the storage corresponds to memory 162 or 262.

The processing circuitry includes at least one of a dedicated hardwareand a program executer, and performs processing using the storage.Furthermore, when the processing circuitry includes the programexecuter, the storage stores a software program to be executed by theprogram executer.

Here, a software for implementing encoder 100, decoder 200, etc.,according to the present embodiment is a program as follows.

In other words, the program may cause a computer to execute an encodingmethod including determining which mode is used to perform theprediction process, among a plurality of modes including a first mode inwhich the prediction process is performed based on a motion vector ofeach block in the video and a second mode in which the predictionprocess is performed based on a motion vector of each sub-block obtainedby splitting the block; when the prediction process is performed in thefirst mode, determining whether to perform a correction process on aprediction image using a spatial gradient of pixel values in theprediction image obtained by performing the prediction process, andperforming the correction process when it is determined to perform thecorrection process; and when the prediction process is performed in thesecond mode, not performing the correction process.

Alternatively, the program may cause a computer to execute a decodingmethod including determining which mode is used to perform theprediction process, among a plurality of modes including a first mode inwhich the prediction process is performed based on a motion vector ofeach block in the video and a second mode in which the predictionprocess is performed based on a motion vector of each sub-block obtainedby splitting the block; when the prediction process is performed in thefirst mode, determining whether to perform a correction process on aprediction image using a spatial gradient of pixel values in theprediction image obtained by performing the prediction process, andperforming the correction process when it is determined to perform thecorrection process; and when the prediction process is performed in thesecond mode, not performing the correction process.

Furthermore, as described above, each component may be a circuit. Thecircuits may be integrated into a single circuit as a whole, or may beseparated from each other. Furthermore, each component may beimplemented as a general-purpose circuit, or as a dedicated circuit.

Furthermore, a process performed by a specific component may beperformed by another component. Furthermore, the order of processes maybe changed, or multiple processes may be performed in parallel.Furthermore, a coding device may include encoder 100 and decoder 200.

The ordinal numbers used in the illustration such as first and secondmay be renumbered as needed. Furthermore, the ordinal number may benewly assigned to a component, etc., or may be deleted from a component,etc.

As described above, the aspects of encoder 100 and decoder 200 have beendescribed based on the embodiment, but the aspects of encoder 100 anddecoder 200 are not limited to this embodiment. Various modifications tothe embodiment that can be conceived by those skilled in the art, andforms configured by combining components in different embodimentswithout departing from the spirit of the present invention may beincluded in the scope of the aspects of encoder 100 and decoder 200.

This aspect may be implemented in combination with one or more of theother aspects according to the present disclosure. In addition, part ofthe processes in the flowcharts, part of the constituent elements of theapparatuses, and part of the syntax described in this aspect may beimplemented in combination with other aspects.

Embodiment 2

As described in each of the above embodiments, each functional block cantypically be realized as an MPU and memory, for example. Moreover,processes performed by each of the functional blocks are typicallyrealized by a program execution unit, such as a processor, reading andexecuting software (a program) recorded on a recording medium such asROM. The software may be distributed via, for example, downloading, andmay be recorded on a recording medium such as semiconductor memory anddistributed. Note that each functional block can, of course, also berealized as hardware (dedicated circuit).

Moreover, the processing described in each of the embodiments may berealized via integrated processing using a single apparatus (system),and, alternatively, may be realized via decentralized processing using aplurality of apparatuses. Moreover, the processor that executes theabove-described program may be a single processor or a plurality ofprocessors. In other words, integrated processing may be performed, and,alternatively, decentralized processing may be performed.

Embodiments of the present disclosure are not limited to the aboveexemplary embodiments; various modifications may be made to theexemplary embodiments, the results of which are also included within thescope of the embodiments of the present disclosure.

Next, application examples of the moving picture encoding method (imageencoding method) and the moving picture decoding method (image decodingmethod) described in each of the above embodiments and a system thatemploys the same will be described. The system is characterized asincluding an image encoder that employs the image encoding method, animage decoder that employs the image decoding method, and an imageencoder/decoder that includes both the image encoder and the imagedecoder. Other configurations included in the system may be modified ona case-by-case basis.

Usage Examples

FIG. 19 illustrates an overall configuration of content providing systemex100 for implementing a content distribution service. The area in whichthe communication service is provided is divided into cells of desiredsizes, and base stations ex106, ex107, ex108, ex109, and ex110, whichare fixed wireless stations, are located in respective cells.

In content providing system ex100, devices including computer ex111,gaming device ex112, camera ex113, home appliance ex114, and smartphoneex115 are connected to internet ex101 via internet service providerex102 or communications network ex104 and base stations ex106 throughex110. Content providing system ex100 may combine and connect anycombination of the above elements. The devices may be directly orindirectly connected together via a telephone network or near fieldcommunication rather than via base stations ex106 through ex110, whichare fixed wireless stations. Moreover, streaming server ex103 isconnected to devices including computer ex111, gaming device ex112,camera ex113, home appliance ex114, and smartphone ex115 via, forexample, internet ex101. Streaming server ex103 is also connected to,for example, a terminal in a hotspot in airplane ex117 via satelliteex116.

Note that instead of base stations ex106 through ex110, wireless accesspoints or hotspots may be used. Streaming server ex103 may be connectedto communications network ex104 directly instead of via internet ex101or internet service provider ex102, and may be connected to airplaneex117 directly instead of via satellite ex116.

Camera ex113 is a device capable of capturing still images and video,such as a digital camera. Smartphone ex115 is a smartphone device,cellular phone, or personal handyphone system (PHS) phone that canoperate under the mobile communications system standards of the typical2G, 3G, 3.9G, and 4G systems, as well as the next-generation 5G system.

Home appliance ex118 is, for example, a refrigerator or a deviceincluded in a home fuel cell cogeneration system.

In content providing system ex100, a terminal including an image and/orvideo capturing function is capable of, for example, live streaming byconnecting to streaming server ex103 via, for example, base stationex106. When live streaming, a terminal (e.g., computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, orairplane ex117) performs the encoding processing described in the aboveembodiments on still-image or video content captured by a user via theterminal, multiplexes video data obtained via the encoding and audiodata obtained by encoding audio corresponding to the video, andtransmits the obtained data to streaming server ex103. In other words,the terminal functions as the image encoder according to one aspect ofthe present disclosure.

Streaming server ex103 streams transmitted content data to clients thatrequest the stream. Client examples include computer ex111, gamingdevice ex112, camera ex113, home appliance ex114, smartphone ex115, andterminals inside airplane ex117, which are capable of decoding theabove-described encoded data. Devices that receive the streamed datadecode and reproduce the received data. In other words, the devices eachfunction as the image decoder according to one aspect of the presentdisclosure.

[Decentralized Processing]

Streaming server ex103 may be realized as a plurality of servers orcomputers between which tasks such as the processing, recording, andstreaming of data are divided. For example, streaming server ex103 maybe realized as a content delivery network (CDN) that streams content viaa network connecting multiple edge servers located throughout the world.In a CDN, an edge server physically near the client is dynamicallyassigned to the client. Content is cached and streamed to the edgeserver to reduce load times. In the event of, for example, some kind ofan error or a change in connectivity due to, for example, a spike intraffic, it is possible to stream data stably at high speeds since it ispossible to avoid affected parts of the network by, for example,dividing the processing between a plurality of edge servers or switchingthe streaming duties to a different edge server, and continuingstreaming.

Decentralization is not limited to just the division of processing forstreaming; the encoding of the captured data may be divided between andperformed by the terminals, on the server side, or both. In one example,in typical encoding, the processing is performed in two loops. The firstloop is for detecting how complicated the image is on a frame-by-frameor scene-by-scene basis, or detecting the encoding load. The second loopis for processing that maintains image quality and improves encodingefficiency. For example, it is possible to reduce the processing load ofthe terminals and improve the quality and encoding efficiency of thecontent by having the terminals perform the first loop of the encodingand having the server side that received the content perform the secondloop of the encoding. In such a case, upon receipt of a decodingrequest, it is possible for the encoded data resulting from the firstloop performed by one terminal to be received and reproduced on anotherterminal in approximately real time. This makes it possible to realizesmooth, real-time streaming.

In another example, camera ex113 or the like extracts a feature amountfrom an image, compresses data related to the feature amount asmetadata, and transmits the compressed metadata to a server. Forexample, the server determines the significance of an object based onthe feature amount and changes the quantization accuracy accordingly toperform compression suitable for the meaning of the image. Featureamount data is particularly effective in improving the precision andefficiency of motion vector prediction during the second compressionpass performed by the server. Moreover, encoding that has a relativelylow processing load, such as variable length coding (VLC), may behandled by the terminal, and encoding that has a relatively highprocessing load, such as context-adaptive binary arithmetic coding(CABAC), may be handled by the server.

In yet another example, there are instances in which a plurality ofvideos of approximately the same scene are captured by a plurality ofterminals in, for example, a stadium, shopping mall, or factory. In sucha case, for example, the encoding may be decentralized by dividingprocessing tasks between the plurality of terminals that captured thevideos and, if necessary, other terminals that did not capture thevideos and the server, on a per-unit basis. The units may be, forexample, groups of pictures (GOP), pictures, or tiles resulting fromdividing a picture. This makes it possible to reduce load times andachieve streaming that is closer to real-time.

Moreover, since the videos are of approximately the same scene,management and/or instruction may be carried out by the server so thatthe videos captured by the terminals can be cross-referenced. Moreover,the server may receive encoded data from the terminals, change referencerelationship between items of data or correct or replace picturesthemselves, and then perform the encoding. This makes it possible togenerate a stream with increased quality and efficiency for theindividual items of data.

Moreover, the server may stream video data after performing transcodingto convert the encoding format of the video data. For example, theserver may convert the encoding format from MPEG to VP, and may convertH.264 to H.265.

In this way, encoding can be performed by a terminal or one or moreservers. Accordingly, although the device that performs the encoding isreferred to as a “server” or “terminal” in the following description,some or all of the processes performed by the server may be performed bythe terminal, and likewise some or all of the processes performed by theterminal may be performed by the server. This also applies to decodingprocesses.

[3D, Multi-Angle]

In recent years, usage of images or videos combined from images orvideos of different scenes concurrently captured or the same scenecaptured from different angles by a plurality of terminals such ascamera ex113 and/or smartphone ex115 has increased. Videos captured bythe terminals are combined based on, for example, theseparately-obtained relative positional relationship between theterminals, or regions in a video having matching feature points.

In addition to the encoding of two-dimensional moving pictures, theserver may encode a still image based on scene analysis of a movingpicture either automatically or at a point in time specified by theuser, and transmit the encoded still image to a reception terminal.Furthermore, when the server can obtain the relative positionalrelationship between the video capturing terminals, in addition totwo-dimensional moving pictures, the server can generatethree-dimensional geometry of a scene based on video of the same scenecaptured from different angles. Note that the server may separatelyencode three-dimensional data generated from, for example, a pointcloud, and may, based on a result of recognizing or tracking a person orobject using three-dimensional data, select or reconstruct and generatea video to be transmitted to a reception terminal from videos capturedby a plurality of terminals.

This allows the user to enjoy a scene by freely selecting videoscorresponding to the video capturing terminals, and allows the user toenjoy the content obtained by extracting, from three-dimensional datareconstructed from a plurality of images or videos, a video from aselected viewpoint. Furthermore, similar to with video, sound may berecorded from relatively different angles, and the server may multiplex,with the video, audio from a specific angle or space in accordance withthe video, and transmit the result.

In recent years, content that is a composite of the real world and avirtual world, such as virtual reality (VR) and augmented reality (AR)content, has also become popular. In the case of VR images, the servermay create images from the viewpoints of both the left and right eyesand perform encoding that tolerates reference between the two viewpointimages, such as multi-view coding (MVC), and, alternatively, may encodethe images as separate streams without referencing. When the images aredecoded as separate streams, the streams may be synchronized whenreproduced so as to recreate a virtual three-dimensional space inaccordance with the viewpoint of the user.

In the case of AR images, the server superimposes virtual objectinformation existing in a virtual space onto camera informationrepresenting a real-world space, based on a three-dimensional positionor movement from the perspective of the user. The decoder may obtain orstore virtual object information and three-dimensional data, generatetwo-dimensional images based on movement from the perspective of theuser, and then generate superimposed data by seamlessly connecting theimages. Alternatively, the decoder may transmit, to the server, motionfrom the perspective of the user in addition to a request for virtualobject information, and the server may generate superimposed data basedon three-dimensional data stored in the server in accordance with thereceived motion, and encode and stream the generated superimposed datato the decoder. Note that superimposed data includes, in addition to RGBvalues, an α value indicating transparency, and the server sets the αvalue for sections other than the object generated fromthree-dimensional data to, for example, 0, and may perform the encodingwhile those sections are transparent. Alternatively, the server may setthe background to a predetermined RGB value, such as a chroma key, andgenerate data in which areas other than the object are set as thebackground.

Decoding of similarly streamed data may be performed by the client(i.e., the terminals), on the server side, or divided therebetween. Inone example, one terminal may transmit a reception request to a server,the requested content may be received and decoded by another terminal,and a decoded signal may be transmitted to a device having a display. Itis possible to reproduce high image quality data by decentralizingprocessing and appropriately selecting content regardless of theprocessing ability of the communications terminal itself. In yet anotherexample, while a TV, for example, is receiving image data that is largein size, a region of a picture, such as a tile obtained by dividing thepicture, may be decoded and displayed on a personal terminal orterminals of a viewer or viewers of the TV. This makes it possible forthe viewers to share a big-picture view as well as for each viewer tocheck his or her assigned area or inspect a region in further detail upclose.

In the future, both indoors and outdoors, in situations in which aplurality of wireless connections are possible over near, mid, and fardistances, it is expected to be able to seamlessly receive content evenwhen switching to data appropriate for the current connection, using astreaming system standard such as MPEG-DASH. With this, the user canswitch between data in real time while freely selecting a decoder ordisplay apparatus including not only his or her own terminal, but also,for example, displays disposed indoors or outdoors. Moreover, based on,for example, information on the position of the user, decoding can beperformed while switching which terminal handles decoding and whichterminal handles the displaying of content. This makes it possible to,while in route to a destination, display, on the wall of a nearbybuilding in which a device capable of displaying content is embedded oron part of the ground, map information while on the move. Moreover, itis also possible to switch the bit rate of the received data based onthe accessibility to the encoded data on a network, such as when encodeddata is cached on a server quickly accessible from the receptionterminal or when encoded data is copied to an edge server in a contentdelivery service.

[Scalable Encoding]

The switching of content will be described with reference to a scalablestream, illustrated in FIG. 20 , that is compression coded viaimplementation of the moving picture encoding method described in theabove embodiments. The server may have a configuration in which contentis switched while making use of the temporal and/or spatial scalabilityof a stream, which is achieved by division into and encoding of layers,as illustrated in FIG. 20 . Note that there may be a plurality ofindividual streams that are of the same content but different quality.In other words, by determining which layer to decode up to based oninternal factors, such as the processing ability on the decoder side,and external factors, such as communication bandwidth, the decoder sidecan freely switch between low resolution content and high resolutioncontent while decoding. For example, in a case in which the user wantsto continue watching, at home on a device such as a TV connected to theinternet, a video that he or she had been previously watching onsmartphone ex115 while on the move, the device can simply decode thesame stream up to a different layer, which reduces server side load.

Furthermore, in addition to the configuration described above in whichscalability is achieved as a result of the pictures being encoded perlayer and the enhancement layer is above the base layer, the enhancementlayer may include metadata based on, for example, statisticalinformation on the image, and the decoder side may generate high imagequality content by performing super-resolution imaging on a picture inthe base layer based on the metadata. Super-resolution imaging may beimproving the SN ratio while maintaining resolution and/or increasingresolution. Metadata includes information for identifying a linear or anon-linear filter coefficient used in super-resolution processing, orinformation identifying a parameter value in filter processing, machinelearning, or least squares method used in super-resolution processing.

Alternatively, a configuration in which a picture is divided into, forexample, tiles in accordance with the meaning of, for example, an objectin the image, and on the decoder side, only a partial region is decodedby selecting a tile to decode, is also acceptable. Moreover, by storingan attribute about the object (person, car, ball, etc.) and a positionof the object in the video (coordinates in identical images) asmetadata, the decoder side can identify the position of a desired objectbased on the metadata and determine which tile or tiles include thatobject. For example, as illustrated in FIG. 21 , metadata is storedusing a data storage structure different from pixel data such as an SEImessage in HEVC. This metadata indicates, for example, the position,size, or color of the main object.

Moreover, metadata may be stored in units of a plurality of pictures,such as stream, sequence, or random access units. With this, the decoderside can obtain, for example, the time at which a specific personappears in the video, and by fitting that with picture unit information,can identify a picture in which the object is present and the positionof the object in the picture.

[Web Page Optimization]

FIG. 22 illustrates an example of a display screen of a web page on, forexample, computer ex111. FIG. 23 illustrates an example of a displayscreen of a web page on, for example, smartphone ex115. As illustratedin FIG. 22 and FIG. 23 , a web page may include a plurality of imagelinks which are links to image content, and the appearance of the webpage differs depending on the device used to view the web page. When aplurality of image links are viewable on the screen, until the userexplicitly selects an image link, or until the image link is in theapproximate center of the screen or the entire image link fits in thescreen, the display apparatus (decoder) displays, as the image links,still images included in the content or I pictures, displays video suchas an animated gif using a plurality of still images or I pictures, forexample, or receives only the base layer and decodes and displays thevideo.

When an image link is selected by the user, the display apparatusdecodes giving the highest priority to the base layer. Note that ifthere is information in the HTML code of the web page indicating thatthe content is scalable, the display apparatus may decode up to theenhancement layer. Moreover, in order to guarantee real timereproduction, before a selection is made or when the bandwidth isseverely limited, the display apparatus can reduce delay between thepoint in time at which the leading picture is decoded and the point intime at which the decoded picture is displayed (that is, the delaybetween the start of the decoding of the content to the displaying ofthe content) by decoding and displaying only forward reference pictures(I picture, P picture, forward reference B picture). Moreover, thedisplay apparatus may purposely ignore the reference relationshipbetween pictures and coarsely decode all B and P pictures as forwardreference pictures, and then perform normal decoding as the number ofpictures received over time increases.

[Autonomous Driving]

When transmitting and receiving still image or video data such two- orthree-dimensional map information for autonomous driving or assisteddriving of an automobile, the reception terminal may receive, inaddition to image data belonging to one or more layers, information on,for example, the weather or road construction as metadata, and associatethe metadata with the image data upon decoding. Note that metadata maybe assigned per layer and, alternatively, may simply be multiplexed withthe image data.

In such a case, since the automobile, drone, airplane, etc., includingthe reception terminal is mobile, the reception terminal can seamlesslyreceive and decode while switching between base stations among basestations ex106 through ex110 by transmitting information indicating theposition of the reception terminal upon reception request. Moreover, inaccordance with the selection made by the user, the situation of theuser, or the bandwidth of the connection, the reception terminal candynamically select to what extent the metadata is received or to whatextent the map information, for example, is updated.

With this, in content providing system ex100, the client can receive,decode, and reproduce, in real time, encoded information transmitted bythe user.

[Streaming of Individual Content]

In content providing system ex100, in addition to high image quality,long content distributed by a video distribution entity, unicast ormulticast streaming of low image quality, short content from anindividual is also possible. Moreover, such content from individuals islikely to further increase in popularity. The server may first performediting processing on the content before the encoding processing inorder to refine the individual content. This may be achieved with, forexample, the following configuration.

In real-time while capturing video or image content or after the contenthas been captured and accumulated, the server performs recognitionprocessing based on the raw or encoded data, such as capture errorprocessing, scene search processing, meaning analysis, and/or objectdetection processing. Then, based on the result of the recognitionprocessing, the server—either when prompted or automatically—edits thecontent, examples of which include: correction such as focus and/ormotion blur correction; removing low-priority scenes such as scenes thatare low in brightness compared to other pictures or out of focus; objectedge adjustment; and color tone adjustment. The server encodes theedited data based on the result of the editing. It is known thatexcessively long videos tend to receive fewer views. Accordingly, inorder to keep the content within a specific length that scales with thelength of the original video, the server may, in addition to thelow-priority scenes described above, automatically clip out scenes withlow movement based on an image processing result. Alternatively, theserver may generate and encode a video digest based on a result of ananalysis of the meaning of a scene.

Note that there are instances in which individual content may includecontent that infringes a copyright, moral right, portrait rights, etc.Such an instance may lead to an unfavorable situation for the creator,such as when content is shared beyond the scope intended by the creator.Accordingly, before encoding, the server may, for example, edit imagesso as to blur faces of people in the periphery of the screen or blur theinside of a house, for example. Moreover, the server may be configuredto recognize the faces of people other than a registered person inimages to be encoded, and when such faces appear in an image, forexample, apply a mosaic filter to the face of the person. Alternatively,as pre- or post-processing for encoding, the user may specify, forcopyright reasons, a region of an image including a person or a regionof the background be processed, and the server may process the specifiedregion by, for example, replacing the region with a different image orblurring the region. If the region includes a person, the person may betracked in the moving picture, and the head region may be replaced withanother image as the person moves.

Moreover, since there is a demand for real-time viewing of contentproduced by individuals, which tends to be small in data size, thedecoder first receives the base layer as the highest priority andperforms decoding and reproduction, although this may differ dependingon bandwidth. When the content is reproduced two or more times, such aswhen the decoder receives the enhancement layer during decoding andreproduction of the base layer and loops the reproduction, the decodermay reproduce a high image quality video including the enhancementlayer. If the stream is encoded using such scalable encoding, the videomay be low quality when in an unselected state or at the start of thevideo, but it can offer an experience in which the image quality of thestream progressively increases in an intelligent manner. This is notlimited to just scalable encoding; the same experience can be offered byconfiguring a single stream from a low quality stream reproduced for thefirst time and a second stream encoded using the first stream as areference.

Other Usage Examples

The encoding and decoding may be performed by LSI ex500, which istypically included in each terminal. LSI ex500 may be configured of asingle chip or a plurality of chips. Software for encoding and decodingmoving pictures may be integrated into some type of a recording medium(such as a CD-ROM, a flexible disk, or a hard disk) that is readable by,for example, computer ex111, and the encoding and decoding may beperformed using the software. Furthermore, when smartphone ex115 isequipped with a camera, the video data obtained by the camera may betransmitted. In this case, the video data is coded by LSI ex500 includedin smartphone ex115.

Note that LSI ex500 may be configured to download and activate anapplication. In such a case, the terminal first determines whether it iscompatible with the scheme used to encode the content or whether it iscapable of executing a specific service. When the terminal is notcompatible with the encoding scheme of the content or when the terminalis not capable of executing a specific service, the terminal firstdownloads a codec or application software then obtains and reproducesthe content.

Aside from the example of content providing system ex100 that usesinternet ex101, at least the moving picture encoder (image encoder) orthe moving picture decoder (image decoder) described in the aboveembodiments may be implemented in a digital broadcasting system. Thesame encoding processing and decoding processing may be applied totransmit and receive broadcast radio waves superimposed with multiplexedaudio and video data using, for example, a satellite, even though thisis geared toward multicast whereas unicast is easier with contentproviding system ex100.

[Hardware Configuration]

FIG. 24 illustrates smartphone ex115. FIG. 25 illustrates aconfiguration example of smartphone ex115. Smartphone ex115 includesantenna ex450 for transmitting and receiving radio waves to and frombase station ex110, camera ex465 capable of capturing video and stillimages, and display ex458 that displays decoded data, such as videocaptured by camera ex465 and video received by antenna ex450. Smartphoneex115 further includes user interface ex466 such as a touch panel, audiooutput unit ex457 such as a speaker for outputting speech or otheraudio, audio input unit ex456 such as a microphone for audio input,memory ex467 capable of storing decoded data such as captured video orstill images, recorded audio, received video or still images, and mail,as well as decoded data, and slot ex464 which is an interface for SIMex468 for authorizing access to a network and various data. Note thatexternal memory may be used instead of memory ex467.

Moreover, main controller ex460 which comprehensively controls displayex458 and user interface ex466, power supply circuit ex461, userinterface input controller ex462, video signal processor ex455, camerainterface ex463, display controller ex459, modulator/demodulator ex452,multiplexer/demultiplexer ex453, audio signal processor ex454, slotex464, and memory ex467 are connected via bus ex470.

When the user turns the power button of power supply circuit ex461 on,smartphone ex115 is powered on into an operable state by each componentbeing supplied with power from a battery pack.

Smartphone ex115 performs processing for, for example, calling and datatransmission, based on control performed by main controller ex460, whichincludes a CPU, ROM, and RAM. When making calls, an audio signalrecorded by audio input unit ex456 is converted into a digital audiosignal by audio signal processor ex454, and this is applied with spreadspectrum processing by modulator/demodulator ex452 and digital-analogconversion and frequency conversion processing by transmitter/receiverex451, and then transmitted via antenna ex450. The received data isamplified, frequency converted, and analog-digital converted, inversespread spectrum processed by modulator/demodulator ex452, converted intoan analog audio signal by audio signal processor ex454, and then outputfrom audio output unit ex457. In data transmission mode, text,still-image, or video data is transmitted by main controller ex460 viauser interface input controller ex462 as a result of operation of, forexample, user interface ex466 of the main body, and similar transmissionand reception processing is performed. In data transmission mode, whensending a video, still image, or video and audio, video signal processorex455 compression encodes, via the moving picture encoding methoddescribed in the above embodiments, a video signal stored in memoryex467 or a video signal input from camera ex465, and transmits theencoded video data to multiplexer/demultiplexer ex453. Moreover, audiosignal processor ex454 encodes an audio signal recorded by audio inputunit ex456 while camera ex465 is capturing, for example, a video orstill image, and transmits the encoded audio data tomultiplexer/demultiplexer ex453. Multiplexer/demultiplexer ex453multiplexes the encoded video data and encoded audio data using apredetermined scheme, modulates and converts the data usingmodulator/demodulator (modulator/demodulator circuit) ex452 andtransmitter/receiver ex451, and transmits the result via antenna ex450.

When video appended in an email or a chat, or a video linked from a webpage, for example, is received, in order to decode the multiplexed datareceived via antenna ex450, multiplexer/demultiplexer ex453demultiplexes the multiplexed data to divide the multiplexed data into abitstream of video data and a bitstream of audio data, supplies theencoded video data to video signal processor ex455 via synchronous busex470, and supplies the encoded audio data to audio signal processorex454 via synchronous bus ex470. Video signal processor ex455 decodesthe video signal using a moving picture decoding method corresponding tothe moving picture encoding method described in the above embodiments,and video or a still image included in the linked moving picture file isdisplayed on display ex458 via display controller ex459. Moreover, audiosignal processor ex454 decodes the audio signal and outputs audio fromaudio output unit ex457. Note that since real-time streaming is becomingmore and more popular, there are instances in which reproduction of theaudio may be socially inappropriate depending on the user's environment.Accordingly, as an initial value, a configuration in which only videodata is reproduced, i.e., the audio signal is not reproduced, ispreferable. Audio may be synchronized and reproduced only when an input,such as when the user clicks video data, is received.

Although smartphone ex115 was used in the above example, threeimplementations are conceivable: a transceiver terminal including bothan encoder and a decoder; a transmitter terminal including only anencoder; and a receiver terminal including only a decoder. Further, inthe description of the digital broadcasting system, an example is givenin which multiplexed data obtained as a result of video data beingmultiplexed with, for example, audio data, is received or transmitted,but the multiplexed data may be video data multiplexed with data otherthan audio data, such as text data related to the video. Moreover, thevideo data itself rather than multiplexed data maybe received ortransmitted.

Although main controller ex460 including a CPU is described ascontrolling the encoding or decoding processes, terminals often includeGPUs. Accordingly, a configuration is acceptable in which a large areais processed at once by making use of the performance ability of the GPUvia memory shared by the CPU and GPU or memory including an address thatis managed so as to allow common usage by the CPU and GPU. This makes itpossible to shorten encoding time, maintain the real-time nature of thestream, and reduce delay. In particular, processing relating to motionestimation, deblocking filtering, sample adaptive offset (SAO), andtransformation/quantization can be effectively carried out by the GPUinstead of the CPU in units of, for example pictures, all at once.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a television receiver, a digitalvideo recorder, a car navigation, a mobile phone, a digital camera, adigital video camera, a teleconference system, an electronic mirror,etc.

1. An encoding method comprising: determining a merge mode to be appliedto a current block, the merge mode including a sub-block merge mode anda first merge mode different from the sub-block merge mode, wherein inthe merge mode, inter-prediction parameters are inferred from aneighboring block neighboring the current block, and in the sub-blockmerge mode, the current block includes a plurality of sub-blocks, andinter-prediction parameters are provided for each of the plurality ofsub-blocks; in response to the merge mode being determined to be thefirst merge mode, generating a prediction image for the current block byperforming a bi-directional optical flow prediction process, wherein thebi-directional optical flow prediction process uses a spatial gradientfor the current block; and in response to the merge mode beingdetermined to be the sub-block merge mode, generating a prediction imagefor the current block by not performing the bi-directional optical flowprediction process.
 2. A decoding method comprising: determining a mergemode to be applied to a current block, the merge mode including asub-block merge mode and a first merge mode different from the sub-blockmerge mode, wherein in the merge mode, inter-prediction parameters areinferred from a neighboring block neighboring the current block, and inthe sub-block merge mode, the current block includes a plurality ofsub-blocks, and inter-prediction parameters are provided for each of theplurality of sub-blocks; in response to the merge mode being determinedto be the first merge mode, generating a prediction image for thecurrent block by performing a bi-directional optical flow predictionprocess, wherein the bi-directional optical flow prediction process usesa spatial gradient for the current block; and in response to the mergemode being determined to be the sub-block merge mode, generating aprediction image for the current block by not performing thebi-directional optical flow prediction process.
 3. A method oftransmitting a bitstream and computer-executable instructions, whereinthe bitstream includes mode information and motion information accordingto which the computer-executable instructions cause a decoder toperform: using the mode information to determine a merge mode to beapplied to a current block, the merge mode including a sub-block mergemode and a first merge mode different from the sub-block merge mode,wherein in the merge mode, inter-prediction parameters are inferred froma neighboring block neighboring the current block, and in the sub-blockmerge mode, the current block includes a plurality of sub-blocks, andinter-prediction parameters are provided for each of the plurality ofsub-blocks; and using the motion information to generate a predictionimage for the current block, wherein, in generating the predictionimage, a bi-directional optical flow prediction process is performed inresponse to the merge mode being determined to be the first merge mode,wherein the bi-directional optical flow prediction process uses aspatial gradient for the current block; and the bi-directional opticalflow prediction process is not performed in response to the merge modebeing determined to be the sub-block merge mode.